John Calvin Commentary Matthew 18:31

"So when his fellow-servants saw what was done, they were exceeding sorry, and came and told unto their lord all that was done." — Matthew 18:31 (ASV)

When his fellow-servants saw what was done. Though we ought not to search for mystery in these words—because they contain nothing but what nature teaches, and what we learn by daily experience—we ought to know that those who live among us will be so many witnesses against us before God. For cruelty will inevitably excite in them displeasure and hatred, especially since every man is afraid that what he sees done to others will fall upon his own head.

As for the clause that immediately follows, it is foolish to inquire how God punishes those sins ⁵⁷⁶ which he has already forgiven. For the simple meaning is this: though he offers mercy to all, yet severe creditors, from whom no forgiveness can be obtained, are unworthy of enjoying it.

⁵⁷⁶ “Comment il est possible que Dieu punisse;” — “how it is possible for God to punish.”;” — “how it is possible for God to punish.”