The Tithe of the Tithe

Numbers 18:25 And the Lord spoke to Moses, saying, 26 “Moreover, you shall speak and say to the Levites, ‘When you take from the people of Israel the tithe that I have given you from them for your inheritance, then you shall present a contribution from it to the Lord, a tithe of the tithe. 27 And your contribution shall be counted to you as though it were the grain of the threshing floor, and as the fullness of the winepress. 28 So you shall also present a contribution to the Lord from all your tithes, which you receive from the people of Israel. And from it you shall give the Lord's contribution to Aaron the priest. 29 Out of all the gifts to you, you shall present every contribution due to the Lord; from each its best part is to be dedicated.’

Just to make sure they understood that being sanctified for service did not mean they were so special they were exempt from tithing or any other acts expected of their fellow Israelites, God explained to the Levites that they too were to give a tithe to the Lord.  They were just as dependent upon God (and maybe more so) and were called to be fully dedicated to God. Whatever privileges God gives us in His service, we never become so special we are exempt from His commands.