In life, it is inevitable that we make mistakes and commit wrong doing.
From the penal perspective, the legal system will prescribe the due punishment for the mistakes and wrong doing, which can be anything from a fine to a jail term.
From the spiritual perspective, there is moral code to adhere to and from that moral code we will know if we have committed any wrong doing, or plainly speaking, we will know if we have sinned.
For us Catholics, when we know we have sinned, we will go for Confession to receive forgiveness and to do penance for our sins.
Yes, God in His mercy and compassion will forgive us our sins and we must atone and make reparation for our sins.
In the Lord's Prayer, there is this phrase: Forgive us our trespasses, as we forgive those who trespasses against us.
So as much as what the scribes and Pharisees said is true, that God alone can forgive us, Jesus also taught us to pray that we forgive those who have wronged us, just as God our Father forgives us our trespasses.
To err is human, to forgive is divine. Let us remember that we are called to be like God, and to forgive others just as we desire to be forgiven.