If you think to yourself, "Hmm...this seems to be more about regeneration than motivation...", my response is: exactly. What I'm trying to show with these quotes from church history is that motivation does not come by rational arguments (outside-in) but by a new disposition implanted in the heart, what Edwards calls a new inner relish (inside-out). Regeneration is the foundation for motivation that is "from the heart" (Rom 6:17).
Charles Haddon Spurgeon (1834-1892), Baptist pastor of the Metropolitan Tabernacle in London:
"[R]egeneration consists in this, God the Holy Spirit, in a supernatural manner—mark, by the word supernatural I mean just what it strictly means; supernatural, more than natural—works upon the hearts of men, and they by the operations of the divine Spirit become regenerate men; but without the Spirit they never can be regenerated. And unless God the Holy Spirit, who ‘worketh in us to will and to do,’ should operate upon the will and the conscience, regeneration is an absolute impossibility, and therefore so is salvation. . . . in the salvation of every person there is an actual putting forth of divine power, whereby the dead sinner is quickened, the unwilling sinner is made willing, the desperately hard sinner has his conscience made tender; and he who rejected God and despised Christ, is brought to cast himself down at the feet of Jesus. . . . If you like it not, quarrel with my Master, not with me; I do but simply declare his own revelation that there must be in your heart something more than you can ever work there. There must be a divine operation, call it a miraculous operation if you please; it is in some sense so. There must be a divine interposition, a divine working, a divine influence, or else do what you may, without that you perish, and are undone—'For except a man be born again he cannot see the kingdom of God.' The change is radical; it gives us new natures, makes us love what we hated and hate what we loved; sets us in a new road; makes our habits different, our thoughts different, makes us different in provate, and different in public."
--The Metropolitan Tabernacle Pulpit: Sermons Preached and Revised by C. H. Spurgeon, 3:188.
"Regeneration is not the reforming of principles which were there before, but the implantation of a something which had no existence; it is the putting into a man of a new thing called the Spirit, the new man – the creation not of a soul, but of a principle higher still – as much higher than the soul, as the soul is higher than the body. . . . In the bringing of any man to believe in Christ, there is as true and proper a manifestation of creating power, as when God made the heavens and the earth."
"The absolute necessity of the new birth is also a certainty. We come down with demonstration when we touch that point. We shall never poison our people with the notion that a moral reformation will suffice, but we will over and over again say to them, 'Ye must be born again.'"
--Lectures to My Students, 222.
Iain Murray discusses Spurgeon on regeneration in The Forgotten Spurgeon (Edinburgh: Banner of Truth Trust, 1966), 95-97.