We usually treat growing up as the whole point. George Herbert, a priest as well as a poet, asks God to let him stay small. In "H. Baptism II" (the "H." presumably short for "Holy", the numeral showing he returned to the subject) he treats his baptism as a head start he never earned, then prays that he will never outgrow it. The central idea is that spiritual health looks like childhood: smallness, softness, dependence. Ordinary growth, by contrast, is a kind of sickness.
The first stanza sets out the reasoning, and it begins with a logical "Since". The way to God is "a narrow way and little gate", an image that echoes the New Testament's narrow gate. A gate that small suits only something small, so God "didst lay hold" of the speaker in infancy and "antedate / My faith in me". Among all these plain words, "antedate" stands out as a piece of paperwork. To antedate a document is to date it earlier than it was written. Faith is credited to the baby before he can possess it, like a cheque written in advance. The rhyme holds the idea in place: "thee" opens the stanza, "me" closes it, and "infancy" sits between them.
The second stanza turns the argument into a request. "Write thee great God, and me a child" is a prayer about names, about the titles he gives God and himself. The adjectives that follow are physical: "soft and supple" suggests leather or a young branch, something that bends instead of snapping. Then comes a balanced line, "Small to my self, to others mild", with humility turned inward and gentleness turned outward. Even the small words carry weight. "Still" means "always" here, though judging by the rest of the poem it may also hint at stillness, at staying put. "Behither ill" is an archaic phrase meaning "on this side of evil". Childhood becomes a border he does not want to cross.
The shape of the stanzas supports this. Each has five lines rhyming *ababa*, and the lengths are roughly four, eight, ten, eight and four syllables. Every stanza swells into a long middle line and then shrinks back to a short one: "My faith in me", "Behither ill", "Childhood is health". The form grows and returns to smallness, which is what the speaker is asking for. Those short last lines also land almost like a door closing.
The third stanza has the sharpest imagery. The flesh advances "by stealth", as if growth were a burglar creeping in while no one is watching. The soul is the flesh's "sister", and the speaker asks that she "bid nothing", which I read as asking nothing and pushing for nothing, and instead "preserve her wealth". That wealth is what baptism has already given. Then comes the blow: "The growth of flesh is but a blister." A blister looks like growth, since it is a swelling, but it is really damage, a bubble of skin with nothing solid inside. Everything we usually admire about getting bigger is recast as an injury.
The closing rhymes press the point. "Stealth", "wealth" and "health" bring the stanza's whole argument into one sound. What sneaks up on us is the thing to fear, and what is worth keeping is the thing we already have. "Childhood is health" is a flat statement, with no decoration and no hedging.
The poem is significant because it turns a worldly value upside down in fifteen lines, and does it in plain speech. Almost every word is a single syllable, so the paradox has nowhere to hide behind ornament. "Childhood" here does not mean ignorance. It means trust, humility and willingness to be held, and the poem is a prayer, so these are things the speaker asks for rather than claims to have. There is a quiet fear underneath, that he might lose by growing what he was given for nothing. A modern reader may not share Herbert's faith, but the poem still makes us notice how automatically we assume that "getting on" is good.