Psalms 141:3

Set a watch, O Lord, before my mouth - While there are so many spies on my actions and words, I have need to be doubly guarded, that my enemies may have no advantage against me. Some think the prayer is against impatience; but if he were now going to Gath, it is more natural to suppose that he was praying to be preserved from dishonoring the truth, and from making sinful concessions in a heathen land; and at a court where, from his circumstances, it was natural to suppose he might be tempted to apostasy by the heathen party. The following verse seems to support this opinion.

Set a watch, O Lord, before my mouth - That I may not say anything rashly, unadvisedly, improperly. Compare Psalm 39:1. The prayer here is, that God would guard him from the temptation to say something wrong. To this he seems to have been prompted by the circumstances of the case, and by the advice of those who were with him. See introduction to the psalm. Compare the notes at Psalm 11:1.

Keep the door of my lips - That my lips or mouth may not open except when it is proper and right; when something good and true is to be said. Nothing can be more proper than "this" prayer; nothing more desirable than that God should keep us from saying what we ought not to say.