He does not say that God will first forgive us, and that we should after forgive our debtors. For God knows how treacherous the heart of man is, and that though they should have received forgiveness themselves, yet they do not forgive their debtors; therefore He instructs us first to forgive, and we shall be forgiven after.
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).