Set a watch, O Lord, before my mouth,.... While praying, as Jarchi and Kimchi; that he might not utter any rash, unguarded, and unbecoming word; but take and use the words which God gives, even the taught words of the Holy Ghost; or lest, being under affliction and oppression, he should speak unadvisedly with his lips, and utter any impatient murmuring and repining word against God; or express any fretfulness at the prosperity of the wicked, or speak evil of them; especially of Saul, the Lord's anointed, for the ill usage of him; keep the door of my lips; which are as a door that opens and shuts: this he desires might be kept as with a bridle, especially while the wicked were before him; lest he should say anything they would use against him, and to the reproach of religion; and that no corrupt communication, or any foolish and filthy talk, or idle and unprofitable words, might proceed from them. The phrase signifies the same as the other; he was sensible of his own inability to keep a proper watch and guard over his words, as was necessary, and therefore prays the Lord to do it; see Psa 39:1.