Forgiveness of others is made an express condition of our obtaining pardon and forgiveness from God (Matt 6:14-15); and the nature hereof is expressly declared (Matt 18:23–35). Such evangelical conditions we have not many. I confess they have no causal influence into the accomplishment of the promise; but the non-performance of them is a sufficient bar against our pretending to the promise, a sufficient evidence that we have no pleadable interest in it. Our forgiving of others will not procure forgiveness for ourselves; but our not forgiving of others proves that we ourselves are not forgiven. And all these things do show what weight God Himself lays on this duty.
The Works of John Owen, 6:496–497.