forgiveness

No, it is not that trivial but far more reaching than we thought.
Lets take a look what God's Word is teaching us.

There are three kinds of forgiveness:
                                               1. Jesus' forgiveness on the cross to offer everyone salvation
                                               2. when our brother repents and asks us for forgiveness
                                               3.  when we forgive a grudge

1.
Ro 6:23 For the wages of sin is death, but the gift of God is eternal life in Christ Jesus our Lord.
Just this one verse makes it clear. One single sin committed by us keeps us from going to heaven and separates us from God for the rest of our life already here on earth.

Isa 59:2 But your iniquities have separated you from your God; your sins have hidden his face from you, so that he will not hear.
Sin separates us from God. Adam and Eve felt this separation physically and spiritually, after they disobeyed and sinned in the Garden of Eden.

God knew, that we could not live without sinning.
Ge 8:21 The LORD ... said: “Never again will I curse the ground because of man, even though every inclination of his heart is evil from childhood."

Therefore God provided a way out, so we can still make it to heaven (Mk 12:25 When the dead rise, .... they will be like the angels in heaven.)  and that is forgiveness. When we ask God to forgive our sins and repent (turn the other direction), HE erases our sin from HIS records and HIS mind.
In the time of Moses, God gave clear commandments and rules about sin and forgiveness. HE established the sacrificial system. By sacrificing an animal without blemish the sinner made atonement for his sin and was thus reconciled to God. But sacrifices had to be made over and over again, because we humans have such a sinful nature.

After God  proved to us that we are not capable of living a sinless life and animals had to be sacrificed constantly, He, by His grace, provided a better way.
Heb 9:26b But now He (Jesus) has appeared once for all at the end of the ages to do away with sin by the sacrifice of Himself. Heb 10:10 And by that will, we have been made holy through the sacrifice of the body of Jesus Christ once for all.
For more detail you may read the whole chapters of Hebrew 9 and 10.

Because Jesus Christ never sinned once in His life, His self sacrifice is so powerful, to make atonement for all of the sins ever committed by man in the past and the future.Through this Christ opened the way into heaven for everyone who repents (Lk15:7) and believes in HIM (John 3:16). But we don't want to forget Christ's further commandment on forgiving:

2.
Mt 6:14 For if you forgive men when they sin against you, your heavenly Father will also forgive you. Mt 6:15 But if you do not forgive men their sins, your Father will not forgive your sins.
Jesus makes it very clear, that if we do not forgive the next person, God will not forgive us and we will than not make it to heaven. Jesus also teaches, that there should be really no limit how often we should forgive another. MT 18:21 Then Peter came and said to Him, “Lord, how often shall my brother sin against me and I forgive him? Up to seven times?” MT 18:22 Jesus *said to him, “I do not say to you, up to seven times, but up to seventy times seven.
EPH 4:32 Be kind to one another, tender-hearted, forgiving each other, just as God in Christ also has forgiven you.

Of course many will wonder now: "But what if the other person never apologizes or asks us for forgiveness?"

3.
If we don't forgive another person, even when he never asks, apologizes or repents, we are keeping the offense in mind and holding a grudge. The resentment builds in us, we are thinking of revenge and even get bitter. Therefore God says:
Lev 19:18 “ ‘Do not seek revenge or bear a grudge against one of your people, but love your neighbor as yourself. I am the LORD.
Eph 4:26 “In your anger do not sin” : Do not let the sun go down while you are still angry, Eph 4:27 and do not give the devil a foothold.
This is all for our own good. When we forgive the next person for an offense before we go to sleep, we are letting God take care of that persons sin. That not only gives us a good night sleep, but also keeps us from sinning by trying revenge on our own. Only the devil is trying to persuade us to revenge, because than he can rule over us.
Pr 17:9 He who covers over an offense promotes love, but whoever repeats the matter separates close friends.

Further more, the grudge that grows to bitterness is like a cancer in our soul, which spills over into our physical body and causes all kinds of illnesses.
Pr 17:22 A cheerful heart is good medicine, but a crushed spirit dries up the bones.

For more on this spirit-health connection go to health & healing on this site.
 

From my own experience I know that a big hurt from another person is first very difficult to overcome but always possible with trust in our unlimited God. I have found, that it is most helpful to pray for the person, which has hurt me, as Jesus has commanded us to pray for our enemies. When I started to practice this, it took me over a year to really get over this particular hurt. During this time so often the "in mind tape player" comes on. I am sure everyone has had this experience where we argue with the other person in our minds. This is a classical access of the devil into our lives. He is the one trying to get a hold on us with lying and accusations. I am getting quicker now to recognize the devils tape player and turn it of with Jesus' words "Get behind me Satan". I then focus on what God has done for me, how He has helped me through the hurt and has prospered me again afterwards. Just like King David has done it in so many of his Psalms and has strengthened himself in the Lord. In the same way we can strengthen ourselves in God by focusing on Him and all the goodness He is giving us daily, starting with the sunrise in the morning, the food, the housing, the closing, .....