Mercy to accept what we do well, and grace to keep us from doing ill, are the two things which we are here taught by David's example to pray to God for.

I.David loved prayer, and he begs of God that his prayers might be heard and answered, Psa 141:1, Psa 141:2. David cried unto God. His crying denotes fervency in prayer; he prayed as one in earnest. His crying to God denotes faith and fixedness in prayer. And what did he desire as the success of his prayer? 1. That God would take cognizance of it: "Give ear to my voice; let me have a gracious audience." Those that cry in prayer may hope to be heard in prayer, not for their loudness, but their liveliness. 2. That he would visit him upon it: Make haste unto me. Those that know how to value God's gracious presence will be importunate for it and humbly impatient of delays. He that believes does not make haste, but he that prays may be earnest with God to make haste. 3. That he would be well pleased with him in it, well pleased with his praying and the lifting up of his hands in prayer, which denotes both the elevation and enlargement of his desire and the out-goings of his hope and expectation, the lifting up of the hand signifying the lifting up of the heart, and being used instead of lifting up the sacrifices which were heaved and waved before the Lord. Prayer is a spiritual sacrifice; it is the offering up of the soul, and its best affections, to God. Now he prays that this may be set forth and directed before God as the incense which was daily burnt upon the golden altar, and as the evening sacrifice, which he mentions rather than the morning sacrifice, perhaps because this was an evening prayer, or with an eye to Christ, who, in the evening of the world and in the evening of the day, was to offer up himself a sacrifice of atonement, and establish the spiritual sacrifices of acknowledgement, having abolished all the carnal ordinances of the law. Those that pray in faith may expect it will please God better than an ox or bullock. David was now banished from God's court, and could not attend the sacrifice and incense, and therefore begs that his prayer might be instead of them. Note, Prayer is of a sweet-smelling savour to God, as incense, which yet has no savour without fire; nor has prayer without the fire of holy love and fervour.

II.David was in fear of sin, and he begs of God that he might be kept from sin, knowing that his prayers would not be accepted unless he took care to watch against sin. We must be as earnest for God's grace in us as for his favour towards us. 1. He prays that he might not be surprised into any sinful words (Psa 141:3): "Set a watch, O Lord! before my mouth, and, nature having made my lips to be a door to my words, let grace keep that door, that no word may be suffered to go out which may in any way tend to the dishonour of God or the hurt of others." Good men know the evil of tongue-sins, and how prone they are to them (when enemies are provoking we are in danger of carrying our resentment too far, and of speaking unadvisedly, as Moses did, though the meekest of men), and therefore they are earnest with God to prevent their speaking amiss, as knowing that no watchfulness or resolution of their own is sufficient for the governing of their tongues, much less of their hearts, without the special grace of God. We must keep our mouths as with a bridle; but that will not serve: we must pray to God to keep them. Nehemiah prayed to the Lord when he set a watch, and so must we, for without him the watchman walketh but in vain. 2. That he might not be inclined to any sinful practices (Psa 141:4): "Incline not my heart to any evil thing; whatever inclination there is in me to sin, let it be not only restrained, but mortified, by divine grace." The example of those about us, and the provocations of those against us, are apt to stir up and draw out corrupt inclinations. We are ready to do as others do, and to think that if we have received injuries we may return them; and therefore we have need to pray that we may never be left to ourselves to practise any wicked work, either in confederacy with or in opposition to the men that work iniquity. While we live in such an evil world, and carry about with us such evil hearts, we have need to pray that we may neither be drawn in by any allurement nor driven on by any provocation to do any sinful thing. 3. That he might not be ensnared by any sinful pleasures: "Let me not eat of their dainties. Let me not join with them in their feasts and sports, lest thereby I be inveigled into their sins." Better is a dinner of herbs, out of the way of temptation, than a stalled ox in it. Sinners pretend to find dainties in sin. Stolen waters are sweet; forbidden fruit is pleasant to the eye. But those that consider how soon the dainties of sin will turn into wormwood and gall, how certainly it will, at last, bite like a serpent and sting like an adder, will dread those dainties, and pray to God by his providence to take them out of their sight, and by his grace to turn them against them. Good men will pray even against the sweets of sin.

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.