This is the great sonnet of Spanish carpe diem, and the model from which, half a century later, Góngora's «Mientras por competir con tu cabello» comes. Garcilaso looks on the beauty of a young woman — the face of rose and lily, the gold hair in the wind — and asks her to seize «the sweet fruit» of her spring before it withers.
The warning comes in the tercets: the «icy wind» of old age will come, snow will cover that rose, and everything will change «so as to make no change in its custom». Garcilaso was the one who naturalised the Italian sonnet and hendecasyllable into Spanish; here that new music, serene and perfect, serves to say the oldest thing of all: that beauty and life come to an end.
The verse is kept in Spanish. Translating it in passing would replace the work with a paraphrase of it.