In the coming days I'll be listing some statements from well-known theologians on Christian motivation and where it comes from.
Francis Turretin (1623-1687), the Swiss theologian known for scholastically formulated Calvinism, says this of regeneration:
"The Spirit in our conversion operates both powerfully and sweetly, pleasingly and invincibly. It pertains to a physical mode that God by his Spirit creates, regenerates, gives us a heart of flesh and infuses into us efficiently the supernatural habits of faith and love. It pertains to a moral mode in that it teaches, inclines, persuades and draws to itself by various reasons as if by the chains of love. Hence Augustine is accustomed everywhere to express it by the phrase 'delightful conqueror' who has conjoined with the highest pleasantness and sweetness, the greatest efficacy and power which expels all the obstinacy of the heart. Thus neither that strength nor efficacy compels the man unwillingly, nor sweetly moves him now running spontaneously; but each joined together both strengthens the weakness of man and overcomes the hatred of sin. It is powerful that it may not be frustrated; sweet that it may not be forced. Its power is supreme and inexpugnable that the corruption of nature may be conquered, as well as the highest impotence of acting well and the necessity of doing evil. Yet still it is friendly and agreeable, such as becomes an intelligent and rational nature . . .
"[U]nless that grace by which we are converted were furnished with the highest power, sin (which has struck its roots so deeply in us) could not be overcome and rooted out. Unless the same would yield fruit of the sweetest joy so that the most loathsome delight of sin might be overcome by the opposite pleasure, the man would be drawn not voluntarily, but unwillingly and in a manner little suited to his nature.
". . . there is always need for a twofold grace in the conversion of man: the one objective and extrinsic, consisting in the proposition of the object; the other subjective, acting immediately upon the faculty to render it capable of receiving the object, not only that it may be able rightly to elicit its own acts in reference to it, but also to elicit them actually. Each depends upon the Holy Spirit working in two ways – both in the word and in the heart; in the word as the objective cause; in the heart as the efficient cause of faith. In the word, acting morally by the revelation of the object and suasion; in the heart, working efficaciously and hyperphysically by an infusion of good habits, the creation of a new heart and the powerful impression of the proposed object."
--Institutes of Elenctic Theology, 2:522-525.