The Lord’s Prayer
Forgive thy neighbour the hurt that he hath done unto thee, so shall thy sins also be forgiven when thou prayest. (Sirach 28:2)
And forgive us our debts, as we forgive our debtors. (Matt 6:12)
This is without a doubt the most intriguing of the New Testament quotations from the Apocrypha, as it forms part of what has come down to us as The Lord’s Prayer, or the Our Father. This is not a pure quotation, but neither is it simply an allusion to the passage from Sirach. Instead, Jesus is inverting the two clauses from Sirach, creating what are parallel statements — a characteristic of Hebrew poetry. The one clause supports and interprets the other. Therefore we cannot interpret the statement from The Lord’s Prayer without referring to its antecedent thought from Sirach.
A typical Protestant understanding of this passage is found in Dr. David P. Scaer’s book, The Sermon on the Mount. He writes:
The Matthean version of the Prayer does not suggest that God’s forgiving us is caused by our forgiving others; the word “as” is used, not “because.” “As” means “like” or “similar.” We ask that God would forgive us ‘as’, not ‘because’ we forgive others. Some hold the view that our forgiving precedes God’s, but this is done more from a theological and not a grammatical consideration.
This is only correct if we do not consider the source for this particular clause in The Lord’s Prayer. In Sirach’s version, forgiveness of the neighbor is necessary for your prayers of forgiveness to be heard. Sirach’s interpretation is demonstrated in Matthew’s gospel by the Parable of the Unforgiving Debtor. (Matt 18:23-34) A servant owed his master a great debt, and asked to be forgiven. When the servant refused to forgive a minor debt owed to him, the master refused to forgive the servant. Jesus sums up the parable by saying: “So likewise shall my heavenly Father do also unto you, if ye from your hearts forgive not every one his brother their trespasses.” (Matt 18:35) Jesus is therefore indicating that the passage from Sirach represents the proper interpretation – that God forgives us when we forgive others.
Blessed Theophylact, in his commentary The Gospel According to St. Matthew, writes:
Because we sin even after our baptism, we beseech Him to forgive us. But forgive us as we forgive others: if we remember wrongs, God will not forgive us. God takes me as the pattern He will follow: what I do to another, He does to me.
God therefore respects our free will. He does not respond in kind, but overabundantly. When we truly repent — when we truly change our mind, rejecting the evil and seeking the good — the angels rejoice, and the Holy Spirit fills us, empowering us for service. But when we seek God half-heartedly, we quench the Holy Spirit, and God seems far from us. It is all God’s work, and none of ours. Nothing we do is meritorious, in and of itself. But God is merciful, bestowing great mercy upon us at the least sign that we are responsive to Him, that we desire communion with Him. This, then, is the meaning of the forgiveness clause in The Lord’s Prayer.
 (D. P. Scaer, The Sermon on the Mount 2000, 184)
 (Blessed Theophylact 1992, 58)