To bless God (Eph. 1:3) does not mean that we contribute anything to the person of God; He is God whether we bless Him, honor Him, acknowledge Him or not. To bless Him means to give thanks and to pronounce Him as being ever worthy of our praise and worship.
To bless God is to be ever-ready to give Him the honor He is due, whether we have received something from Him or not (our worship of Him is not contingent on the reception of benefits from Him). This is how Paul himself applies this truth later in this book:
always giving thanks for all things in the name of our Lord Jesus Christ to God, even the Father (5:20)
Always thankful for all things. That’s what it means to bless God and worship Him. It means that regardless of circumstances, our hearts are ever pre-disposed to worship Him. Whether we receive kind or severe mercies, our hearts are immediately inclined to worship and bless the name of God.
As Calvin well said (which I quoted at the end of my sermon):
Whatever happens to us, let us always assure ourselves that we have good cause to praise our God, and that even if we are poor and miserable in this world, the happiness of heaven is enough to appease us, to sweeten all our afflictions and sorrows, and to give us such content that we may nevertheless have our mouths open to bless God for showing himself so kindhearted and liberal towards us as even to adopt us as his children, and to show us that the heritage which has been purchased for us by the blood of his Son is ready for us, and that we cannot miss it, seeing that we go to it with true and invincible constancy of faith.
Words of Grace 