I think predestination is scary b/c we now know that our futures, what we WANT FOR OURSELVES, is not in our hands but in God's hands. Scary stuff, especially for me being a control freak sometimes and wanting to plan everything according to the way I would like it to turn out and be.
Well, what is comforting is that God protects and will not give us anything that we can't handle or despise. So he may have us doing something that is not necessarily glamrious, but it ends up being fulfilling and exactly what was meant for us.
Honestly, I don't know why Paul is bringing predestination up, maybe because he wants us to know that we have already been given a plan for our lives and instead of walking without Christ, we should walk with and in him so that we may receive the ultimate gift that God has created for us before we were even born.
Maybe he is praising God for it because he knows what God has in store for him/us will be extraordinary and something that is meant for us to fulfill us.