As fast as thou shalt wane, so fast thou grow'st
In one of thine, from that which thou departest,
And that fresh bloud which yongly thou bestow'st,
Thou maist call thine, when thou from youth convertest.
Herein lives wisdome, beauty, and increase,
Without this, follie, age and could decay,
If all were minded so, the times should cease,
And threescoore yeare would make the world away:
Let those whom nature hath not made for store,
Harsh, featurelesse, and rude, barrenly perrish,
Looke whom she best indow'd, she gave the more;
Which bountious guift thou shouldst in bounty cherrish,
So carv'd thee for her seale, and ment therby,
Thou shouldst print more, not let that coppy die.
Changes to original text: Line 1, comma deleted at end of line: Line 4, final comma changed to full stop: Line 6, comma added after 'this'.
In the first quatrain, the poet observes that the young man would grow in his offspring (one of thine) as quickly as he himself degenerates (wane.) The product of his semen (that which thou departest) he may indeed call his when he grows old (from youth convertest).
In the second quatrain, the poet juxtaposes the end results of the two methods of proceeding. The first (herein) produces 'wisdome, beauty, and increase'; the second (without) produces 'follie, age, and could decay', and points out that if everybody thought like the young man, the world would end after seventy years.
In the third quatrain, the poet urges the fair young man to let the ugly perish without issue, while he uses nature's bounty with appropriate bounty.
The final couplet likens the young man to a seal made by nature, who intended him to use his powers to print more like himself.