Of course not. Romans and Galatians don't cancel out Mathew. And Mathew doesn't cancel out Romans and Galatians. But do you suppose that YOU are the one who changes your heart so that you even CAN forgive? If forgiveness was JUST a wise choice, and not something He gives us by changing your heart if you trust Him, then forgiveness would not require God at all.
You do not get to forgiveness by choice. You get to the virtue of forgiveness through trust. The obedience is not :FORGIVE! The obedience is: TRUST!
Does Matthew 6:15 say if you do not trust your fellow men, God will not trust you. No it is talking about forgiveness.
If you forgive, God will forgive you.
If you do not forgive, God will not forgive you. Nothing about "if you trust God". All about the simple (and complex) principle of "if you forgive", then he will forgive, OR if you forgive not, he will forgive not. You make a choice and he follows through with the consequences.
You say: if you trust God, he is the one that will change your heart so that you CAN forgive. OK, I can live with that, but their is still a decision on your part to 'trust' God. So it is not all up to God, you must answer for your own self at some point.
IOW, if I were to have a serious discussion with all the people that showed up to church on Sunday, I would ask them if they trusted in Jesus. How many would say 'yes'? I would guess nearly 100%. Then I would ask that they be honest and tell me if they are holding any type of a grudge against someone in their life that they have not forgiven because they had an evil thing done to them in the past. I would guess around 25% would say they have a bad relationship with someone that they have not forgiven for an evil done to them in the past.
So for this 25%, (who said they trust in God), has God decided not to change their hearts, so they CANNOT forgive, so that he CANNOT forgive them, and their eternal life is in jeopardy. Is that how it works?