2Timothy 3:
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15and that from childhood you have known the sacred writings which are able to give you the wisdom that leads to salvation through faith which is in Christ Jesus.
16All Scripture is inspired by God and
profitable for teaching, for reproof, for correction, for training in righteousness;17so that the man of God may be adequate, equipped for every good work
This does not say that some of the scripture is inspired by God but ALL is not just the New Testament but the Old Testament too. Then it goes on to tell you why..... and if you follow the writings of the OT there is a benefit still today.
All Jesus had to go by in His time on earth was the OT. He trusted and obeyed His Father in Heaven....OT was not all Jews they came after Abraham....just saying....