One reason the Christian message must begin with the God of glory, just as Stephen does in Acts 7, is because sin is ultimately a mighty offense against this God who is glorious and listen how Paul describes sin in Rom. 1:21 For even though they knew God, they did not honor Him as God or give thanks, but they became futile in their speculations, and their foolish heart was darkened. 22 Professing to be wise, they became fools, 23 and exchanged the glory of the incorruptible God for an image in the form of corruptible man and of birds and four-footed animals and crawling creatures (NASB).
Sin is a glory swap with the God of glory being defamed and highly dishonored. When thinking about God in these terms, we are reminded that there is only one God of glory because there is only one God who created all things and possesses all of his attributes which, when viewed as a whole, represent his glory. That’s why there is only one God worthy of worship and full-fledged allegiance. That is the God whom Stephen worships and that is the God who appeared to Abraham. So take note, God isn’t glorious because there is an ornate temple set apart unto him nor even because he called a people to be uniquely his. No, he is the God of glory because of who he is.