Indeed, let me tell you, this is hinge on which our discussion turns, the crucial issue between us; our aim is, simply, to investigate what ability ‘free-will’ has, in what respect it is the subject of Divine action and how it stands related to the grace of God. If we know nothing of these things, we shall know nothing whatsoever of Christianity, and shall be in worse case than any people on earth! He who dissents from that statement should acknowledge that he is no Christian; and he who ridicules or derides it should realise that he is the Christian’s chief fore. For if I am ignorant of the nature, extent and limits of what I can and must do with reference to God, I shall be equally ignorant and uncertain of the nature, extent and limits of what God can and will do in me–though God, in fact, works all in all (cf. I Co. 12.6.). Now, if I am ignorant of God’s works and power, I am ignorant of God himself; and if I do not know God, I cannot worship, praise, give thanks or serve Him, for I do not know how much I should attribute to myself and how much to Him. We need, therefore, to have in mind a clear-cut distinction between God’s power and ours, and God’s work and ours, if we would live a godly life.”
Martin Luther, On The Bondage of the Will (De Servo Arbitrio). In response to Erasmus.