Mark 11:25
And when you stand praying, if you hold anything against anyone, forgive them, so that your Father in heaven may forgive you your sins — the forgiveness condition on effective prayer is the same as the unmerciful servant parable (Matthew 18:23–35). Standing was the normal posture for prayer in Judaism (cf. Luke 18:11). The connection between vertical forgiveness (God forgiving the pray-er) and horizontal forgiveness (the pray-er forgiving others) is the prayer condition: unresolved interpersonal unforgiveness creates the same blockage in prayer that doubt creates.