Set a watch, O Lord, before my mouth - That I may not say anything rashly, unadvisedly, improperly. Compare Psalms 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 Psalms 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.