COMMENTARY on 39:21
A. Yusuf Ali:

Translation:
Seest you not that Allah sends down rain from the sky, and leads it through springs in the earth? 4273 Then He causes to grow, therewith, produce of various colours: then it withers; you wilt seest it grow yellow; then He makes it dry up and crumble away. Truly, in this, is a Message of remembrance to men of understanding.
Commentary:

4273  The circuit of water, by which the rain falls from the clouds, is absorbed through the earth, and flows through rivers or underground streams to the sea, where it again rises as vapour and forms clouds, was explained in notes 311-312 to 25:53. Here our attention is drawn to one portion of the process. The rain fructifies the soil and the seeds. Produce of various kinds is raised. The harvest ripens and is gathered in. The plants wither, dry up, and crumble away. Men and animals are fed. And the circuit starts again in another season.

 

Muhammad Asad:

Translation:
ART THOU NOT aware that it is God who sends down water from the skies, and then causes it to travel through the earth in the shape of springs? And then He brings forth thereby herbage of various hues; and then it withers, and thou canst see it turn yellow; and in the end He causes it to crumble to dust. 26 Verily, in [all] this there is indeed a reminder to those who are endowed with insight!
Commentary:
26  As in many other instances, the above Quranic reference to the endless transformations and the miraculous cycle of life and death in all nature serves to emphasize God’s almightiness and, specifically, His power to resurrect the dead - thus alluding, indirectly, to the statement at the end of the preceding verse that "never does God fail to fulfill His promise".