1 tn Heb “[one of] firm purpose you will keep [in] peace, peace, for in you he possesses trust.” The Hebrew term יֵצֶר (yetser) refers to what one devises in the mind; סָמוּךְ (samukh) probably functions here like an attributive adjective and carries the nuance “firm.” So the phrase literally means, “a firm purpose,” but as the object of the verb “keep, guard,” it must stand by metonymy for the one(s) who possess a firm purpose. In this context the “righteous nation” (v. 2) is probably in view and the “firm purpose” refers to their unwavering faith in God’s vindication (see 25:9). In this context שָׁלוֹם (shalom, “peace”), which is repeated for emphasis, likely refers to national security, not emotional or psychological composure (see vv. 1-2). The passive participle בָּטוּחַ (batuakh) expresses a state that results from the subject’s action.
3 tc The Hebrew text has “for in Yah, the Lord, an everlasting rock.” Some have suggested that the phrase בְּיָהּ (beyah, “in Yah”) is the result of dittography. A scribe seeing כִּי יְהוָה (ki yÿhvah) in his original text would somehow have confused the letters and accidentally inserted בְּיָהּ between the words (bet and kaf [ב and כ] can be confused in later script phases). A number of English versions retain both divine names for emphasis (ESV, NIV, NKJV, NRSV, NLT). One of the Qumran texts (1QIsaa) confirms the MT reading as well.