Why do you have a share in the salvific blessings made to Abraham? On what basis are you right with God and heaven-bound? According to what the Apostle Paul teaches in Gal. 3, both answers are simply by faith in the finished work of Christ.
Based on what we profess, we would be unlikely to admit that adding anything to that gives us a better standing before God, but we can know that we are attempting to add to his work if we are self-righteousness in our attitude towards others. This can happen when we base our righteous status before God on the fact that we have the right theological system, or church background, or devotional time in the Bible or offering amount or prayer time or any other participation in religious things. At that point, we steal glory from Christ and seek to exalt ourselves instead of the glory of God in the gospel.
Furthermore, there’s another way Abraham’s faith is highlighted by what Stephen mentions in Acts 7:1-8. In Heb. 11, the author of Hebrews points out that Abraham’s faith extended beyond receiving the land of Canaan. He actually never received that land; neither did his immediate sons and neither did Moses, but there were all accepted by God due to faith in what God had said. They were sojourners, constantly moving around, and thus they were never able to set their hopes on a physical location. Moreover, they weren’t even buried in the promise land, so clearly they were ultimately hoping in something beyond what was found on this earth. This is crucial to point out because remember a significant percentage of the men sitting in this room listening to Stephen were Sadducees and Sadducees do not believe in the afterlife.
In contrast, Abraham’s hope was not in an earthly location, but it was to be in the presence of God forever.
Interestingly enough, the land of Galilee and Judea had the presence of God in their midst for 30 years, in the incarnation of God the Son, yet they despised him and killed him. It follows that if our hope is set on anything in this world, even if that is a belief system, instead of in what God has promised, then we will end up despising Christ as well, for James writes in James 4:4 that friendship with the world is enmity towards God.
Those who worship the God of glory are to walk in a manner worthy of his calling into that glory and the only way to walk like that is to stand in the grace of God through Christ.