Matthew 18:21-22 meaning

The parallel gospel account of Matthew 18:21-22 is found in Luke 17:4.

Peter then spoke up and asked Jesus to return to the topic of mercy.

Earlier, in what was likely a single conversation or series of conversations spanning from Matthew 17:25 - 18:35, Jesus shared the parable of the lost sheep (Matthew 18:12-14). One of this parable's main points was that God loves His children, and will go after them, even when they stray. Jesus prefaced this parable by telling His disciples that He came to seek and to save that which was lost (Matthew 18:13). And Jesus followed up this parable by instructing his disciples in how to go about trying to restore a brother who had fallen into sin.

Peter asked Jesus, Lord, how often shall my brother sin against me and I forgive him? (v 21). He was asking Jesus where he should draw the limits of his mercy. Peter suggested what he thought was a good answer. "Shall I forgive him up to seven times?" (v 21). His suggestion possibly indicates that Peter was beginning to grasp the mercy principle Jesus taught His disciples in the sermon on the mount (Matthew 5:7; 5:41; 5:44; 6:12; 6:14-15; 7:1-2).

The mercy principle that Jesus taught was that the measure of mercy that we give to others is the same measure of mercy that we receive from God. Peter seems to partially recognize this principle when he asked if he should forgive his brother for sins or offenses done against him up to seven times. Or perhaps Peter is recalling and applying what Jesus said about forgiveness elsewhere.

 "If your brother sins, rebuke him; and if he repents, forgive him. And if he sins against you seven times a day, and returns to you seven times, saying, 'I repent,' forgive him."
(Luke 17:3-4)

Seven times seems pretty generous on Peter's behalf. But Peter is placing limits on mercy and forgiveness, while Jesus was teaching unlimited forgiveness.

Jesus's response to Peter rhetorically and memorably tells him that seven times is far too inadequate. Jesus said to him, I do not say to you, up to seven times, but up to seventy times seven (v 22). Jesus was not teaching Peter to set the limits of his mercy at four hundred and ninety times. Jesus was teaching Peter to set no limits on how much mercy would show. In other words, forgive your brother for sins done against you as many times as your brother needs forgiving. Do not show your brother forgiveness seven times only. Show your brother an infinite amount of mercy and forgiveness.

In the following verses, Jesus teaches Peter a parable to demonstrate this point.