In symmetry with the very first line of the poem.

Again the verb, 'Love,' is separated from the subject, 'Thou and I' through enjambment. By highlighting the words "thou and I," it again emphasizes that the lovers are the core subject of this poem.

Source: Lit Chart https://www.litcharts.com/poetry/john-donne/the-good-morrow

In symmetry with the second to last line of the third stanza.

This enjambment separates the verb, 'Did,' from the subject, 'Thou and I,' as if the speaker is distinguish them from the immature past who are now awaken from it.

Source: Lit Chart https://www.litcharts.com/poetry/john-donne/the-good-morrow

Enjambment : The running-over of a sentence or phrase from one poetic line to the next, without terminal punctuation; the opposite of end-stopped.

Source: Poetry foundation https://www.poetryfoundation.org/learn/glossary-terms/enjambment

enjambment

enjambment