Matthew Poole and continuators on Numbers 1:50

50 But thou shalt appoint the Levites over the tabernacle of testimony , and over all the vessels thereof, and over all things that belong to it: they shall bear the tabernacle, and all the vessels thereof, and they shall minister unto it, and shall encamp round about the tabernacle.

So called here and Exod. 38. 21. because it was made chiefly for the sake of the Ark of the Testimony, 2 Sam. 7. 2. which is oft called the Testimony, as hath been observed before.