I was asked of late --"could it be clearer than Ephes. 1.6 that God simply does what he does for his own glory?" Let's be clear--- the Greek of Ephes. 1.6 says that God does it 'to the praise of his glorious grace'. The Greek preposition is 'eis' here, which is probably not the Greek prepositional equivalent to the English word 'for' here. We would have expected 'pros' if that were the sense here.
More to the point the one praising God's grace here is not God--- that would be us. This whole passage is about doxology-- namely our praising of God for all the gracious things he does and has done for us in Christ, the elect one.
This passage does not tell us what God's motivations were for saving us in Christ. They do however tell us that his actions were so gracious and loving that we all certainly ought to praise and glorify God for his grace.
Furthermore, in the key phrase in this passage the subject is God's grace, not God's glory, which are most certainly distinguishable and distinct ideas. God's wonderful grace is the noun content of this clause, with the word glorious modifying it, which means little more than wonderful or praiseworthy here.
To make this clause some kind of proof text that God does what he does for the sake of his own glory is to read into the text something that simply is not there. God's grace which is to be praised here is God's unmerited favor or undeserved benefit which he lavishes on us. We are praising his other directed love here! God's glory is something else than God's unmerited favor towards us. You will be hard pressed to find a place where Paul suggests that God's motivation for saving us is so God may glorify himself. Clearly enough, this text is not about that.
For more about this see my new Eerdmans commentary on Philemon, Colossians, and Ephesians which is just out.