A.T. Robertson Commentary Acts 1:16

"Brethren, it was needful that the Scripture should be fulfilled, which the Holy Spirit spake before by the mouth of David concerning Judas, who was guide to them that took Jesus." — Acts 1:16 (ASV)

Brethren (ανδρες αδελφο). Literally, men, brethren or brother men. More dignified and respectful than just "brethren." Demosthenes sometimes said Ανδρες Αθηναιο. Cf. our "gentlemen and fellow-citizens." Women are included in this address though ανδρες refers only to men.

It was needful (εδε). Imperfect tense of the impersonal δε with the infinitive clause (first aorist passive) and the accusative of general reference as a loose subject. Peter here assumes that Jesus is the Messiah and finds scripture illustrative of the treachery of Judas. He applies it to Judas and quotes the two passages in verse 20 (Psalms 69:25; Psalms 109:8). The Holy Spirit has not yet come upon them, but Peter feels moved to interpret the situation. He feels that his mind is opened by Jesus (Luke 24:45). It is a logical, not a moral, necessity that Peter points out. Peter here claims the Holy Spirit as speaking in the scriptures as he does in 2 Peter 1:21. His description of Judas as "guide" (οδηγου) to those who seized (συλλαβουσιν) Jesus is that of the base traitor that he was. This very verb occurs in Lu 22:54 of the arrest of Jesus.