Why does God values forgiveness that much? It is because it reflects His character. When we forgive others, we reflect the His love. This is His command: forgive like he has forgiven you. Forgiveness gives us the opportunity to extend to others what God has extended to us.
You are also forgiven by God. Your sin doesn't live here no more. When we forgive others, we show that the Holy Spirit is at work within us. When we forgive, we show that we have not forgotten where He found us.
The alternative to forgiveness is bitterness and resentment. Release that grudge against someone. Forgiveness not only releases us physically and emotionally, it also releases us spiritually. One of the greatest barriers to effective prayer and spiritual vitality is an unforgiving heart (D.L Moody). So, forgive like Christ did to us. Be set free!