When I consider everything that grows
Holds in perfection but a little moment,
That this huge stage presenteth nought but shows
Whereon the stars in secret influence comment;
When I perceive that men as plants increase,
Cheered and checked even by the self-same sky,
Vaunt in their youthful sap, at height decrease,
And wear their brave state out of memory;
Then the conceit of this inconstant stay
Sets you most rich in youth before my sight,
Where wasteful Time debateth with Decay
To change your day of youth to sullied night,
And all in war with Time for love of you,
As he takes from you, I engraft you new.
In plain English
When I look around and see how everything that grows reaches its peak and then fades away in just a moment, and realize that this whole world is just a stage where hidden cosmic forces play out their influence — when I notice that people grow like plants, helped and hindered by the same sky, bursting with youthful energy before they decline and their glory fades from memory.
This thought about how unstable and brief everything is makes me see you standing out, glowing with youth right in front of me. Time and Decay are fighting over you, trying to turn your bright day into a darkened night.
So I'm at war with Time itself, fighting for love of you. As Time steals from you, I preserve you by writing you into my verses.