The phrase you quoted is seemingly contradictory to the gospel of the water and the Spirit. But, you may believe that the Bible is perfect, and has no contradict in it.

Then, is the gospel of the water and the Spirit wrong? No, absolutely not!

Through the entire Word, God shows us that this gospel is the only true and perfect gospel.

There are matches in the Old and New Testament. The sacrificial system in the O.T. is perfectly matches with the eternal sacrifice of Jesus Christ. In sacrificial system, a lawful sacrifice needed three essential conditions: 1) sacrificial animal without blemish, 2) to lay hands on of, 3) blood (vicarious death)

And Jesus Christ, coming to this earth born through the Virgin Mary, as a sinless One, to accept all the sins of the world, was baptized by John the Baptist, the representative of all mankind. Then, He went to the Cross with all the sins of ours, and was crucified to death. But He rose again in three days. We are now forgiven of all our sins (of past, present, and future) by believing this truth that the Lord has completed.

Then, what about the passage "Forgive our trespasses as we forgive those who trespass against us"?

It means that God wants us to forgive each other's insufficiencies. Even though we are born again, we are still in our weak flesh, and do lots of wrongs. If we condemn and rebuke each other of our transgressions then even the power of the true gospel would be fade away, and the fellowship of the born again would be destroyed.

You should take notice that the word 'trespasses' must be corrected into 'debts.' Actually, in the New King James Version it is written: "And forgive us our debts, As we forgive our debtors" (Matthew 6:12).

In Matthew, the Lord's Prayer is directly followed by such teachings as: "For if you forgive men their trespasses, your heavenly Father will also forgive you. But if you do not forgive men their trespasses, neither will your Father forgive your trespasses."

Lord Jesus did not give the Lord's Prayer for us to recite it every day as it is. It is a collection of the important prayer subjects that we should remember in our everyday life of faith.

Please peruse Matthew 18:21-35, then you will reach a understanding of what is the will of God for the unforgiving servant:

"Then Peter came to Him and said, 'Lord, how often shall my brother sin against me, and I forgive him? Up to seven times?' Jesus said to him, 'I do not say to you, up to seven times, but up to seventy times seven. Therefore the kingdom of heaven is like a certain king who wanted to settle accounts with his servants. And when he had begun to settle accounts, one was brought to him who owed him ten thousand talents. But as he was not able to pay, his master commanded that he be sold, with his wife and children and all that he had, and that payment be made. The servant therefore fell down before him, saying, 'Master, have patience with me, and I will pay you all.' Then the master of that servant was moved with compassion, released him, and forgave him the debt. But that servant went out and found one of his fellow servants who owed him a hundred denarii; and he laid hands on him and took him by the throat, saying, 'Pay me what you owe!' So his fellow servant fell down at his feet and begged him, saying, 'Have patience with me, and I will pay you all.' And he would not, but went and threw him into prison till he should pay the debt. So when his fellow servants saw what had been done, they were very grieved, and came and told their master all that had been done. Then his master, after he had called him, said to him, 'You wicked servant! I forgave you all that debt because you begged me. Should you not also have had compassion on your fellow servant, just as I had pity on you?' And his master was angry, and delivered him to the torturers until he should pay all that was due to him. So My heavenly Father also will do to you if each of you, from his heart, does not forgive his brother his trespasses.' "

It means that we always have to forgive our brothers when they sin against us because the Lord already forgave all our past and present and future sins once for all through His baptism and the Cross. Therefore, if we do not forgive our brothers even if the Lord already forgave all their sins on His part, He will be angry with us for our unforgiving mind and will not forgive our sins against our brothers. Only when we forgive our brothers by believing that God already forgave all of us through Jesus' baptism and the Cross, He will be pleased with us.

Therefore the passage can be interpreted like this. "Lord, we forgive our brothers because You already forgave all our sins. Therefore, please do not be angry at our sins." Jesus said like that on the premise He already washed away all the sins of the world. The person who believes like that can forgive his brothers when they sin against him.