Albert Barnes 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)

Men and brethren. This is a customary mode of address, implying affection and respect (Acts 13:26). The Syriac has it more appropriately than by the introduction of the conjunction "and"—"Men, our brethren."

This Scripture. This refers to this portion or prediction contained in the writings of the Old Testament. Scripture, that is, writing. (See Barnes on John 5:39).

The passage to which Peter refers is commonly supposed to be that recorded in Psalm 41:9: Yea, mine own familiar friend—hath lifted up his heel against me. This is expressly applied to Judas by our Saviour in John 13:18. But it seems clear that the reference is not to the 41st Psalm, but to the passage which Peter proceeds to quote in Acts 1:20.

Must needs have been fulfilled. This means it would certainly happen that it would be fulfilled. This was not because there was any physical necessity or compulsion; but it was inevitable that a prediction of God would be fulfilled. This makes no affirmation about the freedom of Judas in doing it. A man will be just as free in wickedness if it is foretold that he will be wicked, as if it had never been known to any other being.

The Holy Ghost, etc. This is a strong attestation to the inspiration of David and accords with the uniform testimony of the New Testament that the sacred writers spake as they were moved by the Holy Ghost (2 Peter 1:21).

Concerning Judas. In what respect this concerned Judas, see Acts 1:20.

Which was guide, etc. (Matthew 26:47; John 18:3).