Albert Barnes Commentary Numbers 8:1-4

"And Jehovah spake unto Moses, saying, Speak unto Aaron, and say unto him, When thou lightest the lamps, the seven lamps shall give light in front of the candlestick. And Aaron did so; he lighted the lamps thereof [so as to give light] in front of the candlestick, as Jehovah commanded Moses. And this was the work of the candlestick, beaten work of gold; unto the base thereof, [and] unto the flowers thereof, it was beaten work: according unto the pattern which Jehovah had showed Moses, so he made the candlestick." — Numbers 8:1-4 (ASV)

The actual lighting of the lamps (compare the marginal references) was to be done to set forth symbolically the special presence which God had now (Numbers 7:89) actually established among His people.