Albert Barnes Commentary Acts 10:11

"and he beholdeth the heaven opened, and a certain vessel descending, as it were a great sheet, let down by four corners upon the earth:" — Acts 10:11 (ASV)

And saw heaven opened. Acts 7:56; see Barnes on Matthew 3:16.

This language is derived from a common mode of speaking in the Hebrew Scriptures, as if the sky above us were a solid, vast expanse, and as if it were opened to present an opportunity for anything to descend. It is language that is highly figurative.

And a certain vessel. See Barnes on Acts 9:15.

As it had been. It is important to note this expression. The sacred writer does not say that Peter literally saw such an object descending, but he uses this as an imperfect description of the vision. It was not a literal descent of a vessel, but it was such a kind of representation to him, producing the same impression and the same effect, as if such a vessel had descended.

Knit at the four corners. Bound, united, or tied. The corners were collected, as would be natural in putting anything into a large sheet.