Hollow with boards shalt thou make it: as it was shewed thee in the mount, so shall they make it.
God set up this altar so His people could meet Him in the court before the tabernacle, where common subjects bring their gifts and priests offer them to the Lord. Wood alone would burn away under divine fire; brass protects it, just as Christ's divine power upholds His human nature against the full weight of God's wrath for our sins.
AI summary
Commenting on Exodus 27:1-8
Hollow with boards shalt thou make it,.... The frame of it being made of boards of shittim wood, there was nothing within side but the grate, which was put within the square, down into the middle of it, and so was light of carriage; though the Targum of Jonathan, and other Jewish writers, represent this hollow as filled up with dust and earth, to answer...
Hollow with boards - It seems to have been a kind of frame-work, and to have had nothing solid in the inside, and only covered with the grating at the top. This rendered it more light and portable.