Thine arrows are sharp - The arrows here may mean the convictions produced in the hearts of men by the preaching of the Gospel. The King is God himself; his enemies are sinners of all sorts. The people, the Jews, thousands of whom were pricked in their hearts under the preaching of Peter and others. All fall before Christ; those who received the word rose again by repentance and faith; those who did not, fell down-all down!
Thine arrows are sharp in the heart - literally, “Thine arrows are sharp - the people under thee shall fall - in the heart of the enemies of the king.” The process of “thought” in the verse seems to be this: First. The “arrows” are seen as sharp or penetrating. Second. The “people” are seen falling as those arrows are shot forth. Third. It is seen that those who fall are the “enemies of the king,” and that the arrows have pierced the “heart.” The word “sharp” is applied to the arrows as denoting that they were adapted to “pierce.” Sometimes arrows are blunted, or with a thick head, rather adapted to smite with force than to wound by penetrating. The bow and the arrow were common instruments in ancient wars, and were mainly used by those who went forth to battle in a chariot. Compare 1 Kings 22:34; 2 Kings 9:21-24. As pertaining to the Messiah, the reference here is, of course, to the “truth,” and to the power of that truth in penetrating the hearts of people. Compare the notes at Hebrews 4:12.
In the heart of the king‘s enemies - That is, the “truths” stated by the Messiah, the conquering king, would penetrate deep into the soul, and slay the sinner, the enemy of the king, that is, of the Messiah. The idea is, that truth would produce an effect in regard to the hopes of the sinner - his self-confidence - his life “as” a sinner - like that which the arrow does when it penetrates the heart. Compare Romans 7:9: “For I was alive without the law once, but when the commandment came, sin revived and I died.” See also the notes at Romans 7:10-11.
Whereby the people fall under thee - As the effect of the arrows; as the effect of truth. The representation is that of victory. As here represented, it is the victory of truth; a conquest by subjecting people to the authority and reign of God.