Responsibility & Inability

I made the point in the sermon from John 6:41-51 that Jesus requires us to repent and believe (v. 47). But it is also true (obnoxiously so according to Spurgeon) that we cannot do it (v. 44) left to our own devices. What are we to make of this conundrum between our responsibility to come and our inability to do so? Shouldn't we be responsible only for what we are able to do and not what we are unable to do?

Wayne Grudem offers this in reply in his one volume systematic theology:

The idea that we are responsible before God only for what we are able to do is contrary to the testimony of Scripture, which affirms both that we “were dead through the trespasses and sins” in which we once walked (Eph. 2:1), and thus unable to do any spiritual good, and also that we are all guilty before God. Moreover, if our responsibility before God were limited by our ability, then extremely hardened sinners, who are in great bondage to sin, could be less guilty before God than mature Christians who were striving daily to obey him. And Satan himself, who is eternally able to do only evil, would have no guilt at all—surely an incorrect conclusion. The true measure of our responsibility and guilt is not our own ability to obey God, but rather the absolute perfection of God’s moral law and his own holiness (which is reflected in that law).

Grudem, W. A. (1994). Systematic Theology : An introduction to Biblical Doctrine (499). Leicester, England; Grand Rapids, Mich.: Inter-Varsity Press; Zondervan Pub. House.