18:34 His lord delivered him to the tormentors - Imprisonment is a much severer punishment in the eastern countries than in ours. State criminals, especially when condemned to it, are not only confined to a very mean and scanty allowance, but are frequently loaded with clogs or heavy yokes, so that they can neither lie nor sit at ease: and by frequent scourgings and sometimes rackings are brought to an untimely end. Till he should pay all that was due to him - That is, without all hope of release, for this he could never do. How observable is this whole account; as well as the great inference our Lord draws from it: The debtor was freely and fully forgiven; He wilfully and grievously offended; His pardon was retracted, the whole debt required, and the offender delivered to the tormentors for ever. And shall we still say, but when we are once freely and fully forgiven, our pardon can never be retracted? Verily, verily, I say unto you, So likewise will my heavenly Father do to you, if ye from your hearts forgive not every one his brother their trespasses.

Matthew 18:34 Parallel Commentaries

On the Words of the Gospel, Matt. xviii. 7, Where we are Admonished to Beware of the Offences of the World.
1. The divine lessons, which we have just heard as they were being read, warn us to gather in a stock of virtues, to fortify a Christian heart, against the offences which were predicted to come, and this from the mercy of the Lord. "For what is man," saith Scripture, "saving that Thou art mindful of him?" [2694] "Woe unto the world because of offences," [2695] saith the Lord; the Truth says so; He alarmeth and warneth us, He would not have us to be off our guard; for surely He would not make us desperate. …
Saint Augustine—sermons on selected lessons of the new testament

The Forgiveness of Sins.
(Twenty-second Sunday after Trinity.) S. MATTHEW xviii. 28, "Pay me that thou owest." The Gospel shows us in a parable a picture of a king who called his servants to a reckoning. That King is the Lord God Almighty. We are His servants, and He calls us to account every day. All we possess we owe as a debt to God. Day by day He gives us our food, and supplies our wants by His good Providence. On every hour of our existence is written, Jehovah-Jireh--The Lord will provide. Day by day God takes …
H. J. Wilmot-Buxton—The Life of Duty, a Year's Plain Sermons, v. 2

Fourth Day. Forgiveness of Injuries.
"Then said Jesus, Father, forgive them; for they know not what they do."--Luke, xxiii. 34. Many a death-struggle has been made to save a friend. A dying Saviour gathers up His expiring breath to plead for His foes! At the climax of His own woe, and of human ingratitude--man-forsaken, and God-deserted--His faltering voice mingles with the shout of His murderers,--"Father, forgive them; for they know not what they do!" Had the faithless Peter been there, could he have wondered at the reply to a former …
John R. Macduff—The Mind of Jesus