This psalm purports to be a Psalm of David, and there is no reason to doubt that it was composed by him, though it is not possible to ascertain why it did not have a place in the collection of his psalms in the early part of the book Ps. 1-72. There are several such, however, scattered through the latter part of the Book of Psalm, leading us to suppose that this which may have been an early collection or "edition" of his psalms, became known as the Psalm of David, and that miscellaneous psalms - and among them not a few of his composition - perhaps later psalms - were subsequently "added" to the volume.
The time when it was composed cannot be ascertained with any certainty or probability. It would "seem" to have been written when he was entering on domestic life, as the psalm consists of "rules" which he appears to have laid down for himself as the head of a family, or as indicating the course which he purposed to pursue in the management of his household. As such, the psalm has a universal application, and may be useful in all times and in all places. Few questions are more important than those which occur to one entering on married life, in regard to his own conduct as the head of a family, to the principles which he shall maintain in his own dwelling, and to the rules by which he shall govern his own conduct. For one in such circumstances it is an inestimable advantage to have an inspired composition like this, indicating what is proper, and suggesting the rules which should guide one in such circumstances.
The psalm consists of the following parts:
I. The introduction - the purpose to praise God with respect to "mercy and judgment;" that is, to make these the theme of his song, Psalm 101:1.
II. His purpose to lead an upright life - a life characterized by wisdom - especially in his own family, Psalm 101:2-3. It is a purpose to "begin" life in this relation aright; "to be" an upright man in his family.
III. The principles on which he purposed to do this, especially in reference to those who should be in his employ as domestics, servants, or laborers, Psalm 101:4-7 :
(1) He would employ no "froward" person, Psalm 101:4.
(2) He would employ no one who was a "slanderer," Psalm 101:5.
(3) He would employ no one who had "a high look or a proud heart," Psalm 101:5.
(4) He would seek out the faithful and the pious in the land to be in his service, Psalm 101:6.
(5) He would employ no one who was deceitful; no one who could not be trusted; no one who was a liar, Psalm 101:7.
IV. These same principles, he says, should govern him in a higher relation - as a sovereign and monarch, for they were principles which were as needful in administering the government of a nation, as in a family; they were principles which a good man should take with him to all the public duties of life, whatever might be his rank, Psalm 101:8. Thus understood, the psalm contains important principles applicable
(a) to man or woman entering on the married life;
(b) to those who are at the head of manufacturing establishments;
(c) to farmers and mechanics;
(d) to those who occupy official positions, and who administer the government of a land - judges, rulers, princes, monarchs.
No better rules could be given to guide those who have others under them or in their employ, in respect to their own conduct, or in respect to those who shall be employed, than such as the psalmist here says should guide him.

The subject proposed, mercy and judgment, Psalm 101:1. The psalmist's resolution in respect to his private conduct, Psalm 101:2. He will put away evil, inward and outward, Psalm 101:3. No evil person shall stand in his presence, Psalm 101:4; nor any slanderer of his neighbor, Psalm 101:4, Psalm 101:5. He will encourage the faithful and upright, Psalm 101:6; but the deceitful, the liars, and the profligate, he will cast out of the city of God, Psalm 101:7, Psalm 101:8.
The Hebrew and all the Versions attribute this Psalm to David. It shows us the resolutions he formed when he came to the throne; and it is a perfect model according to which a wise prince should regulate his conduct and his government.

INTRODUCTION TO PSALM 101
A Psalm of David. The title of this psalm, in the Syriac version, is,
"for Asaph, an exhortation of David, concerning those things which are required in the ministry of the house of the Lord; and a prophecy of the praise of the conqueror, and of the perfect man in God.''
Theodoret thinks it was written by David concerning good Josiah, whom he foresaw, by a spirit of prophecy, would rise up a great reformer of the people, and whom he proposes as a pattern of perfection to others; but it was, no doubt, written by him of himself; very likely, after he was delivered out of his troubles by the death of Saul, and was come to the kingdom, since he resolves to "sing of mercy and judgment": though by the interrogation, "when wilt thou come unto me?" it looks as if he had not arrived to the height of his honour: wherefore, perhaps, this psalm was penned between his being made king over Judah, and his being made king over all the tribes; but, be it as it may, the design of it is to show his resolutions, how he would behave as a king in his court, and as a master in his family; so that it is very instructive to kings and civil magistrates, and to parents and masters of families: and as David was a type of Christ, he seems, throughout the whole, to represent him; and, indeed, there are some things in it which agree with none so well as with him; such as behaving wisely, in a perfect way, and walking in his house with a perfect heart; not suffering any evil thing to cleave unto him, and knowing none, and the like.

David's vow and profession of godliness.