worthy to be praised: said of God as the one people bless, not of a person who has been blessed
Greek had a whole family of words for speaking well of someone: the verb "to bless" (εὐλογέω), the noun "a blessing" (εὐλογία), and this adjective. The adjective is the one that faces upward. It does not describe someone who has been done good; it describes the one whose goodness deserves an answer of praise.
That direction is what English blurs. When the New Testament calls a person "blessed" in the sense of having received God's favor, it uses a form of the verb, as in the welcome "Blessed is he who comes in the name of the Lord." When it says that a person's whole situation is enviable, it reaches for a different word again (μακάριος). This adjective is kept for God: all eight of its appearances have God as their subject, and the one disputed line, Romans 9:5, is disputed precisely because it may stretch the word to cover Christ.
The word arrives in Christian writing already shaped by Jewish prayer, where a blessing opened with "Blessed be the LORD" (the Hebrew בָּרַךְ family). Zechariah's song, Paul, and Peter all reach for that opening, and a letter can also let the same phrase trail after any mention of God, "who is blessed forever, amen." In Mark's account of Jesus before the high priest the adjective goes one step further and stands on its own as a name, "the Son of the Blessed One," a way of pointing at God without pronouncing his name.
Nuances
Whether the praise in Romans 9:5 is predicated of Christ, naming him as God who is blessed forever, or forms a separate ascription of praise to God the Father.
- majorityThe clause belongs with the preceding words about Christ, so Paul calls Christ God, blessed forever. The decisive point is that the adjective follows the noun instead of standing first, which is not how an independent blessing formula runs in Greek.; Bruce M. Metzger, "The Punctuation of Rom. 9:5," in Christ and Spirit in the New Testament, ed. B. Lindars and S. S. Smalley (Cambridge: Cambridge University Press, 1973), 95-112; Murray J. Harris, Jesus as God: The New Testament Use of Theos in Reference to Jesus (Grand Rapids: Baker, 1992); C. E. B. Cranfield, The Epistle to the Romans, ICC, 2 vols. (Edinburgh: T&T Clark, 1975-1979), 2:464-470
- minorityA full stop should be placed before the clause, making it an independent doxology to God the Father, on the ground that Paul nowhere else calls Jesus God outright.; Ezra Abbot, "On the Construction of Romans ix. 5," Journal of the Society of Biblical Literature and Exegesis 1 (1881)