I think if you asked many people what it means to “bless God” an adequate answer would be lacking. Probably for no other reason than it is not a subject we hear preached on at Mass, or study in Catechism class. This is a sad thing to say: we don’t have competent or interested priests and lay catechists doing the work of passing on the revealed religion. Sister Vassa Larin, on the other hand, has provided a brief explanation on the meaning of Blessing God.
“Bless (εὐλόγει) the Lord, O my soul, and let all that is within me bless His holy name. Bless the Lord, O my soul, and forget not all His benefits.” (Ps 102/103: 1-2)
Does God need that I “bless” (εὐ-λόγει, say a good word about) Him? No, of course not. But I need to say “good words” about the Source of Good, the Source of Blessing, lest I forget all His gifts or “benefits,” showered upon me and others every day. I need actively to exercise my God-given capacity for “good words,” even when it is easier to grumble and choose “bad words,” about whatever bad things may cross my path.
The “blessing” (or “good word”) I speak with my mouth, and say in my “soul,” has creative power, because God, my Creator, is the Source of all Blessing. I grow in Him, to be more “like” Him, when I participate or share in His creative energies of “blessing.” Conversely I do damage to my growth, if I choose de-structive, “bad words,” or words that are God-less, outside of God. So let me choose good words today; let me bless, that I may be blessed.