Eight short lines, three vows, one closing explanation: "Son" packs a good deal of parenthood into very little space. The speaker never promises to rescue, advise or protect the boy. They promise instead to suffer alongside him, and to start suffering before anything has gone wrong. Nothing is known here about who wrote the poem or when, so the words on the page have to carry everything, and they carry a lot.
The vows are built the same way each time. A negation opens ("No rest shall i take," "No sleep shall i deserve," "And no good shall i receive"), and an "if" clause follows, naming a disaster: a "runaway," a day of starving, "pain... in your heart held." The consequence comes before the cause. The parent's sleeplessness is announced before the trouble that supposedly triggers it, as if worry has already arrived and is just waiting for a reason. The structure also gives the poem a rocking movement, with a short, firm main clause followed by a longer, looser conditional.
The verbs escalate quietly. To "take" rest is a choice. To "deserve" sleep brings in guilt, as though the son's hunger would make the parent's comfort morally wrong. To "receive" good is to refuse even what the world might hand over unasked. The losses widen as well, from rest to sleep to simply "good." Meanwhile the dangers move inward. Running away is an event anyone could see, starving is a bodily fact, and pain held in the heart may be invisible to everyone but the parent. The vow becomes most total exactly where the speaker is least able to act. There is also no anger anywhere. The son would "happen" to run away or starve, as if by accident, and the parent's reaction contains no blame, only the surrender of ease.
The sound of the poem is plain and loose. The one clear rhyme is "runaway" and "day," in lines two and four. "Deserve" in line three returns as "serves" in line seven, and "serves" pairs with "bears" in the closing couplet, a near-rhyme that tightens the poem just as the real claim arrives. Lines one, five and six stay unrhymed, which keeps the voice closer to speech than to song. There is no fixed meter, and the lines run from five to nine syllables, but the heavy opening beats of "No rest," "No sleep," "no good" give the poem the pulse of a pronouncement.
The language is slightly bent, and the bending matters. "Shall" belongs to oaths. "If you'd happen to make a runaway," "pain is in your heart held" and "which to love me bears" all twist ordinary word order. The effect is formal, almost ritual, though it also makes some lines work harder to understand. Line seven is the best example: "for my life to you only serves." The word "only" can attach either way. My life serves only you, or my life does nothing but serve you. Both readings turn the speaker into a servant of the child's wellbeing. Judging by the lowercase "i" repeated through the poem, the speaker may also be making themselves small, set against the capitalised "You" that begins the last line.
That last line holds the poem's turn. The vows have all been conditional, and now comes a plain statement: "You, my son which to love me bears." The reason for the parent's devotion is given as the son's love, not the parent's own. "Bears" does a lot of work here. It means to carry and to endure, and it is also the verb of giving birth, so the language of parenthood is quietly reversed, with the child now bearing love toward the parent. The poem ends up describing a circuit rather than a one-way sacrifice. The grammar is at its most tangled in this line, which can be read as feeling running ahead of syntax.
What makes "Son" worth reading is its angle on love. It defines love by what the speaker gives up, and the giving up is not heroic action but the inability to be comfortable while someone else is not. The speaker is not identified as mother or father, and that openness lets any parent step into the voice. The poem makes no grand claims. It offers three sleepless promises and a reason, which is perhaps why they sound believable.