2a) I think the scary part of predestination is the fact that we have absolutely no control over being predestined. We are so used to be in control or at least to feel in control of everything and so it is with our spiritual life as well. Now suddenly Paul is saying we are not and have not been in control at all, we are indeed predestined by a sovereign God, according to HIS good pleasure and not our own! And the best is, Paul is praising this sovereign God for it! (see 2d) I think its almost like winning a big competition you haven't even entered for to find out after you have received the big prizes ("spiritual blessings") that you have been chosen to recieve these big prices before the competition even began!
2b) The comforting thing in this predestination, is that we didn't have ANYTHING to do with it and that we are in the hands of a all-loving God who is only interested in our good! And He proved it by sending His own Son to die for us. We are in much better hands than our own!
2c) Paul brings up predestination to press on the Ephesians that firstly they did not have anything to do with their current and future spiritual state and that all praise must go to God for it! It is all His work for His own pleasure. We can only stand in awe over it. Secondly, the church in Ephesus probably consisted of a lot of gentiles and Paul is underlining here that in Christ we are His children both Jew and Gentile.
2d) Paul is praising God for it to impress on the beleivers in Ephesus what wonderful work God has done in their lives without them having anything to do with it. This is the wonderful God we serve! That He chose us regardless and in spite of ourselves! We can only give Him all the praise in reaction to this wonderful fact and really rejoice in it!