The words for bless, blessings, blessed and blessedness, both in the Hebrew and the Greek, are primarily used in scripture two ways.
(1) The first speaks to the idea of a spoken blessings and it effectiveness in terms of lasting impact or immutability.
Such are the blessings which the God speaks in the covenant promises. In Genesis 1:27-28, he not only created Adam and Eve, but he blessed them. The union of our first parents eventually produce Christ the Son of God. The sin which they committed, and the curse of sin upon mankind could not prevent this. In every subsequent blessing which is attached to the covenant promise of our blessings, redemption and our final rest in Christ, the same word (ברך barak)is used in the Hebrew, which are here spoken by Christ as the true inheritance of all the people of God. The blessed are those who in every state and condition are the people of God, it was the promise of all that would be when the YHWH blessed the sabbath day in Gen 2:3, the line of Christ was blessed in Noah and his sons as in Gen 9:1, it was the reality of people from every tongue and tribe and nation which was spoken to Abraham, that in his seed (CHRIST) all the nations of the earth would be BLESSED. Christ was born according to promises given to King David, the promise which he claimed as BLESSINGS from the LORD in 2 Samuel 7:28-29.
(2) The second way bless is used is as a state of being.
The blessed in this context as Christ is teaching the disciples the BLESSED are BLESSED, BECAUSE. All blessings come from the LORD:
“Blessed be the God and Father of our Lord Jesus Christ, who has blessed us with every spiritual blessing in the heavenly places in Christ, just as He chose us in Him before the foundation of the world, that we should be holy and without blame before Him in love, having predestined us to adoption as sons by Jesus Christ to Himself, according to the good pleasure of His will, to the praise of the glory of His grace, by which He made us accepted in the Beloved.” (Eph 1:3–6)