Behold, they belch out with their mouth - The word rendered "belch out" means properly to boil forth; to gush out, to flow; and then, to pour forth copiously, or in a running stream, as a fountain does. Hence, the word means also to pour out "words" - words that flow freely - words of folly, abuse, or reproach. Proverbs 15:2, "the mouth of fools poureth out (Margin, belcheth or babbleth) foolishness." Proverbs 15:28, "the mouth of the wicked poureth out evil things;" that is, "gushes over" with wicked things - as a fountain overflows. In this place, the word means that the enemies of David who were in pursuit of his life, poured out reproaches and threatenings like a gushing fountain.
Swords are in their lips - Their words are as sharp swords. See the notes at Psalm 57:4.
For who, say they, doth hear? - That is, no one hears who will be able to punish us. They dread no man; and they have no fear of God. Compare the notes at Psalm 10:11. The words "say they" are, however, supplied here by the translators, and are not in the original; and the language "may" be understood as that of David himself, "as if" no one heard; that is, It is no wonder that they thus pour out words of reproach, for who "is" there to hear and to punish them? The former interpretation, however, is to be preferred. The language expresses the feelings of the enemies of David, who indulged freely in language of abuse and reproach "as if" there were none to hear.

They belch out with their mouth - They use the lowest insult, the basest abuse. They deal in sarcasm, ridicule, slander, and lies.

Behold, they (f) belch out with their mouth: swords [are] in their lips: for who, [say they], doth hear?
(f) They boast openly in their wicked devises, and every word is as a sword: for they neither fear God nor are ashamed of men.

Behold, they belch out with their mouth,.... Bark like dogs, so Aben Ezra; or "bubble out" (u), as a fountain bubbles out with water; so they cast out their wickedness in great abundance; see Jeremiah 6:7; the phrase denotes the abundance of evil things and wicked speeches that came out of their mouths, which showed the naughtiness of their hearts; so David's enemies blustered and threatened what they would do to him could they find him; and Christ's enemies poured out their wicked charges of blasphemy and sedition against him, in great plenty, and without proof;
swords are in their lips; the words of their lips were like sharp swords; see Psalm 55:21; threatening the most severe and cruel things: or, besides their lips, and what they belched out with their mouths, they took swords in their hands in a literal sense; as Saul's messengers did to kill David, and as Judas and his band of men, who came to take Christ as a thief, with swords and staves, Matthew 26:55;
for who, say they, doth hear? what they uttered with their mouths and lips, in a blustering and threatening manner; though they were overheard by men, who carried what they said and designed to do to Michal, David's wife. The meaning may be, they would say what they pleased, and did not care who heard them, having nothing to fear from any, they having their orders from the king; see Psalm 12:4; and so the Targum,
"behold they belch out with their mouths words which are sharp as swords, and with their lips saying, we shall prevail; for who is he that hears, and can punish?''
Aben Ezra's note is,
"they thought that God did not hear their counsels;''
and therefore the next words are in direct opposition to them; but so to think is monstrous stupidity and brutishness, Psalm 94:4; some take the words to be the words of David, complaining that the civil magistrate, none of the judges, took notice of or punished such who belched out their lies and calumnies against him, saying, "for who doth hear?" no man.
(u) "scaturient", Montanus; "copiose eructant", Gejerus.

for who, say they--For the full expression with the supplied words, compare Psalm 64:5.

Pour out - Sharp and bitter word's, abundantly and vehemently, as a fountain doth waters, as this word signifies. Swords - Words as keen and mischievous as swords. For who - David doth not hear us, and God either doth not hear, or not regard what we say.