Adam Clarke on Revelation 7:1

And after these things - Immediately after the preceding vision.

I saw four angels - Instruments which God employs in the dispensation of his providence; we know not what.

On the four corners of the earth - On the extreme parts of the land of Judea, called ἡ γη, the land, or earth, by way of eminence.

Holding the four winds - Preventing evil from every quarter. Earth - sea, nor on any tree; keeping the whole of the land free from evil, till the Church of Christ should wax strong, and each of his followers have time to prepare for his flight from Jerusalem, previously to its total destruction by the Romans.