Numbers 4:39
From thirty years old and upward even unto fifty years old, every one that entereth into the service, for the work in the tabernacle of the congregation, From thirty years old and upward even unto fifty years old, every one that entereth into the service, for the work in the tabernacle of the congregation,
Numbers 4:39 concerns the Levites' appointed service in the tabernacle. That work included erecting the tabernacle and encamping around it. When Israel journeyed, the same service required taking the tabernacle down and carrying it, together with the ark, the candlestick, and the other sacred furnishings.