The repetitions are emphatic; expressive of anxious love.
Son of my vows - Like Samuel, and Samson, the child often asked for in prayer, the prayer ratified by a vow of dedication. The name Lemuel (literally "for God," consecrated to Him) may be the expression of that dedication; and the warning against indulging in wine Proverbs 31:4 shows that it had something of the Nazarite or Rechabite idea in it.

What, my son? - The Chaldee בר bar is used twice in this verse, instead of the Hebrew בן ben, son. This verse is very elliptical; and commentators, according to their different tastes, have inserted words, indeed some of them a whole sentence, to make up the sense. Perhaps Coverdale has hit the sense as nearly as any other: "These are the wordes of Kynge Lemuel; and the lesson that his mother taughte him. My sonne, thou son of my body, O my deare beloved sonne!"
The son of my vows? - A child born after vows made for offsprings is called the child of a person's vows.

What, my son? and what, the son of (c) my womb? and what, the son of my vows?
(c) By this often repetition of one thing, she declares her motherly affection.

What, my son?.... What shall I call thee? though thou art a king, can I address thee in more suitable language, or use a more endearing appellative than this, and what follows? permit me, thy mother, to speak unto thee as my son: and what shall I say to thee? I want words, I want wisdom; O that I knew what to say to thee, that would be proper and profitable; or what is it I am about to say to thee? things of the greatest moment and importance, and therefore listen to me; and so the manner of speaking is designed to excite attention: or what shall I ask of thee? no part of thy kingdom, or any share in the government of it; only this favour, to avoid the sins unbecoming a prince, and to do the duty of a king, later mentioned. The Targum and Syriac version represent her as exclaiming, reproving, and threatening; as, Alas my son! is this the life thou designest to live, to give up thyself to wine and women? fie upon it, my son, is this becoming thy birth, education, and dignity? is this the fruit of all the pains I have taken in bringing thee up? consider the unbecoming part thou art acting;
and what, the son of my womb? whom I bore in sorrow, brought forth in pain, and took so much care and trouble to bring up in a religious way, and form for usefulness in church and state? not an adopted son, but my own flesh and blood; and therefore what I say must be thought to proceed from pure affection to thee, and solely for thy good; see Isaiah 49:15;
and what, the son of my vows? whom I asked of God, and promised to give up to him again, and did; for which reason she might call him Lemuel, as Hannah called her son Samuel, for a like reason, 1-Samuel 1:28; a son for whom she had put up many prayers, for his temporal and spiritual good; and on whose account she had made many vows, promises, and resolutions, that she would do so and so, should she be so happy as to bring him into the world, and bring him up to man's estate, and see him settled on the throne of Israel.

What, my son?--that is, What shall I say? Repetitions denote earnestness.
son of my womb--as our phrase, "my own son," a term of special affection.
son of my vows--as one dedicated to God; so the word "Lemuel" may mean.

2 What, my son? and what the son of my womb?
And what, O son of my vows?!
The thrice repeated מה is completed by תּעשׂה (cf. Khler under Malachi 2:15), and that so that the question is put for the purpose of exciting attention: Consider well, my son, what thou wilt do as ruler, and listen attentively to my counsel (Fleischer). But the passionate repetition of מה would be only affectation if thus interpreted; the underlying thought must be of a subjective nature: what shall I say, אדבּר (vid., under Isaiah 38:15), what advise thee to do? The question, which is at the same time a call, is like a deep sigh from the heart of the mother concerned for the welfare of her son, who would say to him what is beneficial, and say it in words which strike and remain fixed. He is indeed her dear son, the son whom she carries in her heart, the son for whom with vows of thanksgiving she prayed to God; and as he was given her by God, so to His care she commits him. The name "Lemuel" is, as we interpret it, like the anagram of the fulfilment of the vows of his mother. בּרי bears the Aramaic shade in the Arameo-Arab. colouring of these proverbs from Massa; בּריהּ is common in the Aram., and particularly in the Talmudic, but it can scarcely be adduced in support of ברי. וּמה belongs to the 24, מה, with ח or ע not following; vid., the Masora to Exodus 32:1, and its correction by Norzi at Deuteronomy 29:23. We do not write וּמה־בּר; מה, with Makkeph and with Metheg, exclude one another.

What - A short speech, arguing her great passion for him; what words shall I take? What counsels shall I give thee? My heart is full, but where shall I begin? Of my womb - My son, not by adoption, but whom I bare in the womb, and therefore it is my duty to give thee admonitions, and thine to receive them. My vows - On whose behalf I have made many prayers and sacrifices, and solemn vows to God; whom I have, as far as in me lay, devoted to the work, and service, and glory of God.