Text: 2 Timothy 3:15-17
. . . and how from infancy you have known the Holy Scriptures, which are able to make you wise for salvation through faith in Christ Jesus. All Scripture is God-breathed and is useful for teaching, rebuking, correcting and training in righteousness, so that the servant of God may be thoroughly equipped for every good work.
Christians read the whole Bible, Old Testament and New Testament.
My uncle Rudy's story about elder who took over his class because he was using new NIV (1970s) and opened the Bible saying, "This half matters. This half doesn't."
Marcion was a church father who thought the Old Testament didn't matter. Unfortunately some of our heritage is marcionite in how we approach the Old Testament.
Paul was talking about the Old Testament when he was writing to Timothy!
So, the Old Testament (and New Testament) is useful for training, rebuking, correcting, training in righteousness.