1 Kings 8:3 - Matthew Poole's English Annotations on the Holy Bible

For although the Levites might do this, Numbers 4:15, yet the priests did it at this time, partly for the greater honour of the solemnity, and partly because the Levites might not enter into the holy place, much less into the holy of holies, where it was to be placed, into which the priests themselves might not have entered, if the high priest alone could have done it. Object. The Levites are said to have done this, 2 Chronicles 5:4. Answ. That is most true, because all the priests were Levites, though all the Levites were not priests.