Yea, he sent out his arrows - The word arrows here probably refers to the lightnings mentioned in the other clause of the verse. Those lightnings scattered around, and accomplishing such destruction, seemed to be arrows sent forth from the hand of God.
And scattered them - Herder refers this to the lightnings; DeWette, to the enemies of the psalmist. The latter seems to be the more correct interpretation, though the enemies of the psalmist are not here particularly specified. They seem, however, to have been in his eye throughout the psalm, for it was the victory achieved over them by the divine interposition that he was celebrating throughout the poem.
And he shot out lightnings - As arrows; or, as from a bow.
And discomfited them - literally, to impel, to drive; then, to put in commotion or consternation. The allusion is to an army whose order is disturbed, or which is thrown into confusion, and which is, therefore, easily conquered. The idea is that David achieved a victory over all his enemies, as if God had scattered them by a storm and tempest.

Be sent out his arrows - he shot out lightning - I believe the latter clause to be an illustration of the former. He sent out his arrows - that is, he shot out lightning; for lightnings are the arrows of the Lord, and there is something very like the arrowhead apparent in the zigzag lightning. Sense and sound are wonderfully combined in the Hebrew of this last clause: וברכים רב ויהמם uberakim rab vaihummem, "and thunderings he multiplied and confounded them." Who does not hear the bursting, brattling, and pounding of thunder in these words? See Delaney?

Yea, he sent out (k) his arrows, and scattered them; and he shot out lightnings, and discomfited them.
(k) His lightening.

Yea, he sent out his arrows,.... By which thunderbolts, cracks of thunder, and flashes of lightning, seem to be meant; see Psalm 77:17; comparable to arrows shot, and sent out of a bow; and may denote, either the doctrines of the Gospel, which were sharp in the hearts of Christ's enemies, and are either the means of subduing them to him, or of destroying them, being the savour of death unto death; or however, like arrows, give great pain and uneasiness where they stick, and grievously distress and torment; as does the fire which comes out of the mouth of the two witnesses, Revelation 11:5. The Targum is,
"he sent his word as arrows;''
or else the judgments of God are meant, as famine, pestilence, and the sword, which God sent unto, and spent upon the Jewish nation, Deuteronomy 32:23;
and scattered them; among the nations of the world, where they have been dispersed ever since;
and he shot out lightnings; or "many lightnings", so the Targum:
and discomfited them; troubled, terrified, and distressed them.

The fiery brightness of lightning, in shape like burning arrows rapidly shot through the air, well represents the most terrible part of an awful storm. Before the terrors of such a scene the enemies are confounded and overthrown in dismay.

Arrows - Lightnings. Them - Mine enemies.