Full work is at http://www.ccel.org/b/bernard/loving_god/index.html
You want me to tell you why God is to be loved and how much. I answer, the reason for loving God is God Himself; and the measure of love due to Him is immeasurable love. Is this plain? Doubtless, to a thoughtful man; but I am debtor to the unwise also. A word to the wise is sufficient; but I must consider simple folk too. Therefore I set myself joyfully to explain more in detail what is meant above.
We are to love God for Himself, because of a twofold reason; nothing is more reasonable, nothing more profitable. When one asks, Why should I love God? he may mean, What is lovely in God? or What shall I gain by loving God? In either case, the same sufficient cause of love exists, namely, God Himself.
And first, of His title to our love. Could any title be greater than this, that He gave Himself for us unworthy wretches? And being God, what better gift could He offer than Himself? Hence, if one seeks for God's claim upon our love here is the chiefest: Because He first loved us (I John 4:19).
Ought He not to be loved in return, when we think who loved, whom He loved, and how much He loved? For who is He that loved? The same of whom every spirit testifies: 'Thou art my God: my goods are nothing unto Thee' (Ps. 16:2, Vulg.). And is not His love that wonderful charity which 'seeketh not her own'? (I Cor.13:5). But for whom was such unutterable love made manifest? The apostle tells us: 'When we were enemies, we were reconciled to God by the death of His Son' (Rom. 5:10). So it was God who loved us, loved us freely, and loved us while yet we were enemies. And how great was this love of His? St. John answers: 'God so loved the world that He gave His only-begotten Son, that whosoever believeth in Him should not perish, but have everlasting life' (John 3:16). St. Paul adds: 'He spared not His own Son, but delivered Him up for us all' (Rom. 8:32); and the son says of Himself, 'Greater love hath no man than this, that a man lay down his life for his friends' (John 15:13).
This is the claim which God the holy, the supreme, the omnipotent, has upon men, defiled and base and weak. Some one may urge that this is true of mankind, but not of angels. True, since for angels it was not needful. He who succored men in their time of need, preserved angels from such need; and even as His love for sinful men wrought wondrously in them so that they should not remain sinful, so that same love which in equal measure He poured out upon angels kept them altogether free from sin.
Love is one of the four natural affections, which it is needless to name since everyone knows them. And because love is natural, it is only right to love the Author of nature first of all. Hence comes the first and great commandment, 'Thou shalt love the Lord thy God.' But nature is so frail and weak that necessity compels her to love herself first; and this is carnal love, wherewith man loves himself first and selfishly, as it is written, 'That was not first which is spiritual but that which is natural; and afterward that which is spiritual' (I Cor. 15:46). This is not as the precept ordains but as nature directs: 'No man ever yet hated his own flesh' (Eph. 5:29). But if, as is likely, this same love should grow excessive and, refusing to be contained within the restraining banks of necessity, should overflow into the fields of voluptuousness, then a command checks the flood, as if by a dike: 'Thou shalt love thy neighbor as thyself'. And this is right: for he who shares our nature should share our love, itself the fruit of nature. Wherefore if a man find it a burden, I will not say only to relieve his brother's needs, but to minister to his brother's pleasures, let him mortify those same affections in himself, lest he become a transgressor. He may cherish himself as tenderly as he chooses, if only he remembers to show the same indulgence to his neighbor. This is the curb of temperance imposed on thee, O man, by the law of life and conscience, lest thou shouldest follow thine own lusts to destruction, or become enslaved by those passions which are the enemies of thy true welfare. Far better divide thine enjoyments with thy neighbor than with these enemies. And if, after the counsel of the son of Sirach, thou goest not after thy desires but refrainest thyself from thine appetites (Ecclus. 18:30); if according to the apostolic precept having food and raiment thou art therewith content (I Tim. 6:8), then thou wilt find it easy to abstain from fleshly lusts which war against the soul, and to divide with thy neighbors what thou hast refused to thine own desires. That is a temperate and righteous love which practices self-denial in order to minister to a brother's necessity. So our selfish love grows truly social, when it includes our neighbors in its circle.
But if thou art reduced to want by such benevolence, what then? What indeed, except to pray with all confidence unto Him who giveth to all men liberally and upbraideth not (James 1:5), who openeth His hand and filleth all things living with plenteousness (Ps. 145:16). For doubtless He that giveth to most men more than they need will not fail thee as to the necessaries of life, even as He hath promised: 'Seek ye the Kingdom of God, and all those things shall be added unto you' (Luke 12:31). God freely promises all things needful to those who deny themselves for love of their neighbors; and to bear the yoke of modesty and sobriety, rather than to let sin reign in our mortal body (Rom. 6:12), that is indeed to seek the Kingdom of God and to implore His aid against the tyranny of sin. It is surely justice to share our natural gifts with those who share our nature.
But if we are to love our neighbors as we ought, we must have regard to God also: for it is only in God that we can pay that debt of love aright. Now a man cannot love his neighbor in God, except he love God Himself; wherefore we must love God first, in order to love our neighbors in Him. This too, like all good things, is the Lord's doing, that we should love Him, for He hath endowed us with the possibility of love. He who created nature sustains it; nature is so constituted that its Maker is its protector for ever. Without Him nature could not have begun to be; without Him it could not subsist at all. That we might not be ignorant of this, or vainly attribute to ourselves the beneficence of our Creator, God has determined in the depths of His wise counsel that we should be subject to tribulations. So when man's strength fails and God comes to his aid, it is meet and right that man, rescued by God's hand, should glorify Him, as it is written, 'Call upon Me in the time of trouble; so will I hear thee, and thou shalt praise Me' (Ps. 50:15). In such wise man, animal and carnal by nature, and loving only himself, begins to love God by reason of that very self-love; since he learns that in God he can accomplish all things that are good, and that without God he can do nothing.
So then in the beginning man loves God, not for God's sake, but for his own. It is something for him to know how little he can do by himself and how much by God's help, and in that knowledge to order himself rightly towards God, his sure support. But when tribulations, recurring again and again, constrain him to turn to God for unfailing help, would not even a heart as hard as iron, as cold as marble, be softened by the goodness of such a Savior, so that he would love God not altogether selfishly, but because He is God? Let frequent troubles drive us to frequent supplications; and surely, tasting, we must see how gracious the Lord is (Ps. 34:8). Thereupon His goodness once realized draws us to love Him unselfishly, yet more than our own needs impel us to love Him selfishly: even as the Samaritans told the woman who announced that it was Christ who was at the well: 'Now we believe, not because of thy saying: for we have heard Him ourselves, and know that this is indeed the Christ, the savior of the world' (John 4:42). We likewise bear the same witness to our own fleshly nature, saying, 'No longer do we love God because of our necessity, but because we have tasted and seen how gracious the Lord is'. Our temporal wants have a speech of their own, proclaiming the benefits they have received from God's favor. Once this is recognized it will not be hard to fulfill the commandment touching love to our neighbors; for whosoever loves God aright loves all God's creatures. Such love is pure, and finds no burden in the precept bidding us purify our souls, in obeying the truth through the Spirit unto unfeigned love of the brethren (I Peter 1:22). Loving as he ought, he counts that command only just. Such love is thankworthy, since it is spontaneous; pure, since it is shown not in word nor tongue, but in deed and truth (I John 3:18); just, since it repays what it has received. Whoso loves in this fashion, loves even as he is loved, and seeks no more his own but the things which are Christ's, even as Jesus sought not His own welfare, but ours, or rather ourselves. Such was the psalmist's love when he sang: 'O give thanks unto the Lord, for He is gracious' (Ps. 118:1). Whosoever praises God for His essential goodness, and not merely because of the benefits He has bestowed, does really love God for God's sake, and not selfishly. The psalmist was not speaking of such love when he said: 'So long as thou doest well unto thyself, men will speak good of thee'(Ps. 49:18). The third degree of love, we have now seen, is to love God on His own account, solely because He is God.
How blessed is he who reaches the fourth degree of love, wherein one loves himself only in God! Thy righteousness standeth like the strong mountains, O God. Such love as this is God's hill, in the which it pleaseth Him to dwell. 'Who shall ascend into the hill of the Lord?' 'O that I had wings like a dove; for then would I flee away and be at rest.' 'At Salem is His tabernacle; and His dwelling in Sion.' 'Woe is me, that I am constrained to dwell with Mesech!' (Ps. 24:3; 55:6; 76:2; 120:5). When shall this flesh and blood, this earthen vessel which is my soul's tabernacle, attain thereto? When shall my soul, rapt with divine love and altogether self-forgetting, yea, become like a broken vessel, yearn wholly for God, and, joined unto the Lord, be one spirit with Him? When shall she exclaim, 'My flesh and my heart faileth; but God is the strength of my heart and my portion for ever' (Ps. 73:26). I would count him blessed and holy to whom such rapture has been vouchsafed in this mortal life, for even an instant to lose thyself, as if thou wert emptied and lost and swallowed up in God, is no human love; it is celestial. But if sometimes a poor mortal feels that heavenly joy for a rapturous moment, then this wretched life envies his happiness, the malice of daily trifles disturbs him, this body of death weighs him down, the needs of the flesh are imperative, the weakness of corruption fails him, and above all brotherly love calls him back to duty. Alas! that voice summons him to re-enter his own round of existence; and he must ever cry out lamentably, 'O Lord, I am oppressed: undertake for me' (Isa. 38:14); and again, 'O wretched man that I am! who shall deliver me from the body of this death?' (Rom. 7:24).
Seeing that the Scripture saith, God has made all for His own glory (Isa. 43:7), surely His creatures ought to conform themselves, as much as they can, to His will. In Him should all our affections center, so that in all things we should seek only to do His will, not to please ourselves. And real happiness will come, not in gratifying our desires or in gaining transient pleasures, but in accomplishing God's will for us: even as we pray every day: 'Thy will be done in earth as it is in heaven' (Matt. 6:10). O chaste and holy love! O sweet and gracious affection! O pure and cleansed purpose, thoroughly washed and purged from any admixture of selfishness, and sweetened by contact with the divine will! To reach this state is to become godlike. As a drop of water poured into wine loses itself, and takes the color and savor of wine; or as a bar of iron, heated red-hot, becomes like fire itself, forgetting its own nature; or as the air, radiant with sun-beams, seems not so much to be illuminated as to be light itself; so in the saints all human affections melt away by some unspeakable transmutation into the will of God. For how could God be all in all, if anything merely human remained in man? The substance will endure, but in another beauty, a higher power, a greater glory. When will that be? Who will see, who possess it? 'When shall I come to appear before the presence of God?' (Ps. 42:2). 'My heart hath talked of Thee, Seek ye My face: Thy face, Lord, will I seek' (Ps. 27:8). Lord, thinkest Thou that I, even I shall see Thy holy temple?
In this life, I think, we cannot fully and perfectly obey that precept, 'Thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy strength, and with all thy mind' (Luke 10:27). For here the heart must take thought for the body; and the soul must energize the flesh; and the strength must guard itself from impairment. And by God's favor, must seek to increase. It is therefore impossible to offer up all our being to God, to yearn altogether for His face, so long as we must accommodate our purposes and aspirations to these fragile, sickly bodies of ours. Wherefore the soul may hope to possess the fourth degree of love, or rather to be possessed by it, only when it has been clothed upon with that spiritual and immortal body, which will be perfect, peaceful, lovely, and in everything wholly subjected to the spirit. And to this degree no human effort can attain: it is in God's power to give it to whom He wills. Then the soul will easily reach that highest stage, because no lusts of the flesh will retard its eager entrance into the joy of its Lord, and no troubles will disturb its peace. May we not think that the holy martyrs enjoyed this grace, in some degree at least, before they laid down their victorious bodies? Surely that was immeasurable strength of love which enraptured their souls, enabling them to laugh at fleshly torments and to yield their lives gladly. But even though the frightful pain could not destroy their peace of mind, it must have impaired somewhat its perfection.