The Hebrew term barak and its derivatives convey the idea of ”blessing.” The root means “knee”, so some interpret the word “blessed” to be derived from the act of kneeling in worship or receiving a blessing from him. In the Hebrew mentality, speaking of blessing was thought of as an act through which the person received power to obtain success, prosperity, fertility, longevity, etc.
Bliss is, then, a state of happiness. The term “blessed” is almost always used as an expression equivalent to “happy that one”. Thus, in the song of Moses, it is said: “Blessed are you, O Israel, who is like you, a people saved by the Lord” (Deu 33:29). The queen of Sheba, after seeing the glory of Solomon, exclaimed: “Blessed are your men, blessed are these your servants…” (1 Kings 10:8). It is in this sense that the term is used in other portions, such as Ps 1:1 (“Blessed is the man who did not walk in the counsel of wicked men”).
Lord Jesus spoke of eight blessed in Mat 5:3-11 (“those who are poor in spirit”, … “those who mourn”, … “the meek”, … “those who hunger and thirst for righteousness”, … “the merciful † , … †œthe pure in heart† , … †œpeacemakers† , … †œthose who are persecuted for the sake of justice† ). In Luke 6:20-23 they appear as blessed “the poor…. Those of you who are hungry right now… you who now mourn….† and also those whom men “hate, and when they separate you from themselves, and revile you, and reject your name as evil, because of the Son of Man† .
man addresses God, calling him “Blessed” (“the blessed and only Sovereign, King of kings, and Lord of lords”), or “blessed” (“Blessed be the God and Father of our Lord Jesus Christ”), is expressing worship and acknowledging that he is the source of “every good gift and every perfect gift” (James 1:17).
Source: Christian Bible Dictionary