CS Lewis:
Though natural likings should normally be encouraged, it would be quite wrong to think that the way to become charitable is to sit trying to manufacture affectionate feelings. Some people are ‘cold’ by temperament; that may be a misfortune for them, but it is no more a sin than having a bad digestion is a sin; and it does not cut them out from the chance, or excuse them from the duty, of learning charity. The rule for all of us is perfectly simple. Do not waste time bothering whether you ‘love’ your neighbor; act as if you did. As soon as we do this we find one of the great secrets. When you are behaving as if you loved someone, you will presently come to love him. If you injure someone you dislike, you will find yourself disliking him more. If you do him a good turn, you will find yourself disliking him less. There is, indeed, one exception. If you do him a good turn, not to please God and obey the law of charity, but to show him what a fine forgiving chap you are, and to put him in your debt, and then sit down to wait for his ‘gratitude’, you will probably be disappointed. (People are not fools: they have a very quick eye for anything like showing off, or patronage.) But whenever we do good to another self, just because it is a self, made (like us) by God, and desiring its own happiness as we desire ours, we shall have learned to love it a little more or, at least, to dislike it less.

Consequently, though Christian charity sounds a very cold thing to people whose heads are full of sentimentality, and though it is quite distinct from affection, yet it leads to affection. The difference between a Christian and a worldly man is not that the worldly man has only affections or ‘likings’ and the Christian has only ‘charity’. The worldly man treats certain people kindly because he ‘likes’ them: the Christian, trying to treat every one kindly, finds himself liking more and more people as he goes on — including people he could not even have imagined himself liking at the beginning.    (see more at here)

(I’m fascinated by this 1884 articulation of the different types of people there are—and of his wonderful pushing the more amiable towards biblical love.)

The love produced by the Holy Spirit is not a love which comes out of men on account of their natural constitution. I have known persons who are tenderly affectionate by nature—and this is good, but it is not spiritual love—that is the fruit of nature and not of Grace! An affectionate disposition is admirable, but it may become a danger by leading to inordinate affection, a timid fear of offending, or an idolatry of the creature.  I do not condemn natural amiability—on the contrary, I wish that all men were naturally amiable—but I would not have any person think that this will save him, or that it is a proof that he is renewed.
Only the love which is the fruit of the Spirit may be regarded as a mark of Grace. Some people, I am sorry to say, are naturally sour—they seem to have been born at the season of crabapples and to have been fed on vinegar. They always take a fault-finding view of things. They never see the sun’s splendor and yet they are so clear-sighted as to have discovered his spots. They have a great specialty of power for discerning things which it were better not to see. They do not remember that the earth has proved steady and firm for centuries, but they have a lively recollection of the earthquake, and they quake, even now, as they talk about it.  Such as these have need to cry for the indwelling of the Spirit of God, for if He will enter into them His power will soon overcome the tendency to sourness, for, “the fruit of the Spirit is love.” Spiritual love is nowhere found without the Spirit and the Spirit is nowhere dwelling in the heart unless love is produced.

Love is consequent upon God’s unfathomable love and infinite mercy towards us.  For Paul this was foundational:
I live by faith in the Son of God, who loved me and gave Himself for me. (Galatians 2:20)

The result of the transforming, sanctifying ministry of the Holy Spirit in our lives is just this: that we are enabled to love one another with the same kind of love that God loves us.

Paul profiled this kind of love in 1 Corinthians 13; it is a love that “seeks not its own”.

–all from Timothy George

It cannot be overemphasized that for the Christian, love has already been given him.  In the new birth he has already been “created after God,” “he has been raised to newness of life.”  Hence sanctification is not imposing a new conduct on an individual, it is providing a climate, or an environment in which the newly planted seed will germinate and appear.  –John Sanderson

and finally, JI Packer: Regeneration is birth; sanctification is growth. In regeneration, God implants desires that were not there before: desire for God, for holiness, and for the hallowing and glorifying of God’s name in this world; desire to pray, worship, love, serve, honor, and please God; desire to show love and bring benefit to others. In sanctification, the Holy Spirit “works in you to will and to act” according to God’s purpose; what he does is prompt you to “work out your salvation” (i.e., express it in action) by fulfilling these new desires (Phil. 2:12-13). Christians become increasingly Christlike as the moral profile of Jesus (the “fruit of the Spirit”) is progressively formed in them (2 Cor. 3:18; Gal. 4:19; 5:22-25). Paul’s use of glory in 2 Corinthians 3:18 shows that for him sanctification of character is glorification begun. Then the physical transformation that gives us a body like Christ’s, one that will match our totally transformed character and be a perfect means of expressing it, will be glorification completed (Phil. 3:20-21; 1 Cor. 15:49-53).