The theme of this poem is that growing old is difficult because a person loses their looks and their abilities. Faith in God, however, can provide some consolation during these changes. The speaker of the poem calls his silver hair the "harbingers" of old age. He is disappointed that "they have [his] brain," and, he fears, they will "turn [him] to a clod" because growing old means losing one's quickness and sharp wit.

He refers to the practice of sending "forerunners" ahead of a monarch's progress through the kingdom to find lodgings for everyone in the king or queen's household. These forerunners would mark the doorways of those homes and inns that offered appropriate rooms with white chalk so that those places could be identified later on when the monarch's entourage came through. The speaker compares the white hairs on his head to these marks, betokening the coming of someone significant, perhaps God himself.

The speaker says that his "lovely metaphors" will leave him, though he has given God his "best." He suggests that he has prepared his best "rooms" for God, that he has offered God the very best he could produce during his lifetime. Thus, he feels somewhat prepared for the coming "winter," a metaphor for old age and death, and will make the most of what he has left so that his final years can be even "livelier than before."

The dominant theme of "The Forerunners" is the onset of old age. But as with all of Herbert's poems the ostensible theme ultimately reflects the individual believer's relationship to God. As with other Metaphysical poets, Herbert uses a conceit, an elaborate metaphor, to convey his underlying message. In this case, the approach of old age is likened to the arrival of forerunners, advance parties sent out to find suitable accommodation for a royal entourage before a visit. Once they'd found somewhere to stay, the forerunners would mark the doors of chosen properties with white chalk. Herbert compares this ritual to the little crop of white hair starting to grow upon his ageing head:

The harbingers are come. See, see their mark:

White is their colour, and behold my head.

But must they have my brain? Must they dispark

Those sparkling notions, which therein were bred?

Must dullness turn me to a clod?

Yet have they left me, Thou art still my God.

George Herbert (1593-1633), one of the metaphysical poets, wrote quiet and precise devotional verse. "The Forerunners" is no exception. In it the poet ruminates on the coming of old age (hence the title) -

His reflections are shot through with ambivalence: He regrets that advancing age brings with it enfeeblement, the gradual loss of his ability to write poetry. Yet, at the same time, he expresses gratitude that his versifying faculty can still express the motto, "Thou art still my God". He summarizes this sentiment in the second stanza of the poem: