According as he hath chosen us in him before the foundation of the world, that we should be holy and without blame before him in love:
Note 4 at Eph 1:4: The phrase "according as" means "corresponding to the way in which" (American Heritage Dictionary). Paul was explaining to what degree we have been blessed with all spiritual blessings (Eph 1:3). It goes beyond our ability to conceive.
We were chosen in Christ before the world began. We are holy and without blame because God sees us through Christ. We have had it predetermined that we will be God's children (Eph 1:5). We have been accepted by God (Eph 1:6). We are redeemed and forgiven (Eph 1:7). We have all of God's wisdom and prudence (Eph 1:8). The mysteries of God have been revealed to us (Eph 1:9). We are truly blessed!
Note 5 at Eph 1:4: The Lord did not choose us on our merit, but solely on our acceptance of Christ. His foreknowledge (see note 1 at Ro 8:29) allowed Him to make before that choice the foundation of the world. In the strictest sense, we were not personally chosen; Christ was chosen, and all those who are "in Christ" partake of His being chosen by His Father. Just as we are the beneficiaries of the covenant between God the Father and His Son, Jesus (see note 4 at Ga 3:29), so are we chosen because we chose God's chosen; i.e., Christ. The Father would no more reject us than He would reject Jesus, because we are accepted by the Father through Christ (Eph 1:6).
Note 6 at Eph 1:4: This verse reveals that God the Father had the plan of salvation worked out before He even created the world. Most of us would not have created the world and man if we knew the heartache and terrible sacrifice that act would cost. God is not man, and in His judgment (which is the correct judgment), the prize was worth all the cost.
Note 7 at Eph 1:4: None of us can claim that we are without blame in the sight of man, because man looks on the outward appearance (1Sa 16:7) and all of us have sinned (Ro 3:23). The Lord looks on our born-again spirits, which have been regenerated in Christ, and He sees us holy and without blame.
If you look through a red glass, everything becomes red. The same thing would happen if you looked through a green glass; everything would become green. In a similar way, God looks at us through Christ, and everything in our lives becomes covered by the blood of Jesus. We are holy and without blame before Him because of His love expressed through His Son.