And when ye stand praying, forgive, if ye have ought against any: that your Father also which is in heaven may forgive you your trespasses.
-- Mark 11:25
Forgiving others, including ourselves, is a key to effective prayer. If we harbor ill feelings against others, it is like throwing a wet blanket on our prayers. It smothers them as it buries us under a mountain of negativity and bitterness. God cannot engage with us unless He forgives us, and He will not forgive us if we do not forgive others.
Forgiveness is not an easy act. When we have been wronged or hurt, it is hard to forgive the perpetrator; but when the wrong or hurt has been done to someone we love, forgiveness can be nearly impossible. It may very well be the work of a lifetime to come to genuine forgiveness for those who have deeply hurt us and our loved ones.
The natural man in each of us hates forgiveness. He wants revenge, and if he can't have it, he loves the poison of unrequited offense. He gleefully wallows in the mire of spite, anger, and a deserved grudge. He relishes a good feud that can be passed around and bequeathed to our children and their children.
Our challenge is to overcome the natural man, so the spiritual child in each of us can have room to grow. If forgiveness does not come easily, do not despair. Pray to God to forgive your unforgiving heart and ask in sincerity for the gift of forgiveness toward others.
As Jesus promised, "For verily I say unto you, That whosoever shall say unto this mountain, Be thou removed, and be thou cast into the sea; and shall not doubt in his heart, but shall believe that those things which he saith shall come to pass; he shall have whatsoever he saith. Therefore I say unto you, What things soever ye desire, when ye pray, believe that ye receive them, and ye shall have them" (Mark 11:23-24). The mountain you may need to move may be labeled "bitterness, resentment, grievance, hard feelings," but Jesus promised you can move it, and He is willing to help.