For if you forgive men their trespasses,
Your heavenly Father will also forgive you.
But if you do not forgive men their trespasses,
Neither will your Father forgive your trespasses.”
Jesus then adds a rider, stressing the kind of people that they must be if their Father is to have dealings with them in a continuing forgiveness (note the emphasis of His words here on God as their Father). If they are to see God as their Father, and enjoy His continual forgiveness, they must be those who, like Him, love their enemies, and who are peacemakers. The blessings of the Kingly Rule of Heaven (which include God's continual forgiveness) are for those who are truly under the Kingly Rule of Heaven. How could they be otherwise? Thus those who would enjoy them must themselves be under the Kingly Rule of Heaven and thus be involved in dispensing the forgiveness of the new age (Matthew 18:21-22). Indeed they cannot be Jesus' disciples and yet not be involved in being forgiving. For being unforgiving is as bad as clinging on to riches. It sets them against God.
The point is thus that if they are not willing to reveal themselves as true sons of their Father (Matthew 5:9; Matthew 5:45) by being forgiving to those who seek their forgiveness, they cannot very well expect to be treated as such. They have proved that they are not. Forgiving others is not seen here as a condition of their being forgiven, it is rather seen as a ‘not without which'. It is seen as one of the signs that give them right of entry to their Father. That is, it is an indication that they are of those who walk rightly with God and as such can therefore expect forgiveness from their Father.
So Jesus is not saying here that they will be forgiven if they forgive. That would be impossible. Forgiveness from God cannot be bargained for, nor can it be earned. He is saying rather that if they want God to treat them as His sons by forgiving them, their grosser sins, they must be revealing in their lives that they are true sons by forgiving others their lesser sins. It is not a tit for tat, otherwise we might as well give up. If God's forgiveness was dependent on the level of ours we would have no hope. What is in mind is that our hearts are revealed as having the right attitude. We can compare with this how they are also to be reconciled with those who have things against them before they bring their gifts to God (Matthew 5:23-24). In both cases they must approach God having put behind them all that might offend God. How could someone with the spirit of the servant in Matthew 18:23-30 possibly approach Someone like the God of infinite mercy and compassion?
‘Trespasses.' Note that here ‘debts' has now become ‘trespasses', confirming that the ideas are synonymous. The principle described here is so important that it is repeated in Matthew 18:23-35 where the new community is being described. It also occurs in a different context in Mark 11:25.
There is an interesting parallel to this in Sir 28:1-2, ‘he who takes vengeance will find vengeance from the Lord, and He will surely make firm his sins. Forgive your neighbour the hurt that he has done you, and then your sins will be pardoned when you pray'. The same principle lies behind it. It is caught up in the basic principle, ‘you shall love your neighbour as yourself'. But whereas in Ecclesiasticus ‘neighbour' probably meant very much their fellow Jews, with Jesus the requirement was to forgive ‘men and women'. It was universal.