"For the serious mistakes, he offered his Son to pay for all those sins that will inevitably occur."
To pay whom, precisely?
And why does this person need to be paid?
No unclean thing can enter into the presence of God (see Rev 21:27). The payment is not due to a person, it is due to the concept of justice. If you sin, justice demands that you be excluded from the presence of God. Jesus was punished for sins he never committed. That was unjust. To satisfy justice, God ceded the right to extend mercy (not being punished for something you did do) to Jesus. Jesus has the right to forgive sins committed (mercy) and return you to the presence of God. You still have free will. You can accept the forgiveness or go your own way. Unlike the retail stores, this one doesn't come with a 30 day free trial. You have to make the decision for yourself.