Charles Spurgeon Commentary Numbers 8:5-6

"And Jehovah spake unto Moses, saying, Take the Levites from among the children of Israel, and cleanse them." — Numbers 8:5-6 (ASV)

These men were to be the servants of God; they are the type of God's elect—a people set apart for divine service, to be zealous for good works. Take the Levites from among the children of Israel, and cleanse them. That is just the way that God the Holy Ghost takes Christians from among mankind, and cleanses them.