Is the Old Testament relevant?
Was God more wrathful in the Old Testament times than He is today?
No. Today God is just as wrathful as then. Sodom and Gomorrah show that he will deal with what is sinful. He is a God of extreme power! But because of His love and mercy (which balance his justice and wrath) he allows us time to repent and find him.
Australia has 80,000 abortions a year. This invites God’s wrath. God is merciful, but there is a limit.
Do we have to keep the 10 Commandments?
When we accept Jesus, the 10 Commandments (the Law) no longer bind us, because under grace we are forgiven. Indeed, with a changed heart and the Holy Spirit within us, we find that we now naturally want to obey the Law. We are no longer bound or forced to obey it, but free to obey it.