He follows this up by stating a very basic principle with which none can conceivably argue: to the man who works for a reward and earns it, that reward is not accounted to him as a gracious gift, but as a debt.  It is like the position of a man who holds a job; that man does not thank the employer when he receives his paycheck at the end of the week.  After all, he worked for it; he traded his time and labor for the monetary reward he is given.  The man who works for salvation, if (hypothetically speaking) he successfully earned it, would have no reason to give everlasting praise to the grace of God.  He would be able to frankly say in the presence of God Himself, “I need give no thanks for divine grace; I worked for this reward, and I have earned it by the goodness of my conduct.”  God would owe such a man salvation, if he had behaved himself so perfectly as to earn the reward of salvation.

But that was not the case with Abraham, nor can it be the case with any sinner.  God is no man’s debtor, and certainly will not be so in the realm of salvation.  Only the proudest Pharisee could imagine standing in the blazing light of God’s glory, and attempting to claim the reward of eternal life based upon his own immaculate conduct.  Of course, such a man could no more be received than that Pharisee who prayed in the temple opposite the publican in our Lord’s parable.  The righteousness which he cherished so much is naught but filthy rags, and can never purchase admittance into God’s heaven.