Charles Ellicott Commentary Mark 11:25-26

"And whensoever ye stand praying, forgive, if ye have aught against any one; that your Father also who is in heaven may forgive you your trespasses. [But if ye do not forgive, neither will your Father who is in heaven forgive your trespasses.]" — Mark 11:25-26 (ASV)

And when you stand praying, forgive.—See Notes on Matthew 6:14. The reproduction of the words which are recorded as having been spoken in the Sermon on the Mount is very significant. The prayer even of intensest faith is not perfect, unless the temper of the worshipper is also that of the Charity which forgives offences. Such words exclude from the prayers of Christ’s disciples wishes more or less vindictive, which, as in Psalms 69 and 109, had seemed natural and right under a less perfect manifestation of the will and mind of the Father.