Therefore, be sure that it is those who are of faith who are sons of Abraham I am sorry I don't nderstand how this follows what I said. We believe in the same God, the God of Abraham, but that does not mean that Moses or Abraham were Christians.
Moses and Abraham are believers saved by faith. Paul was a believer saved by faith. Titus was a believer saved by faith. The distinction I'm trying to make is that Moses, Abraham, Paul and Titus might have held different "labels" (Jew, Christian, Gentile, etc) but they were all of the same faith chosen by God in exactly the same manner. We are related to Moses and Abraham simply based upon our faith. For a scriptural reference to this I would refer you to the following passage:
Rom 9:6-8 ...For they are not all Israel who are descended from Israel; nor are they all children because they are Abraham's descendants, but: "THROUGH ISAAC YOUR DESCENDANTS WILL BE NAMED." That is, it is not the children of the flesh who are children of God, but the children of the promise are regarded as descendants.