Redeem the firstborn which belong to the Lord

Numbers 3:14-51
Count the Levites by their families and clans, the Lord said to Moses in the Desert of Sinai.
Gershon : the number of all the males a month old or who were counted was 7,500. They responsible for the are of the tabernacle and tent.
Kohath were responsible for the care of the sanctuary was 8,600.
Merari : The number of all the males a month old or who were counted was 6,200. They were appointed to take care of the frames of the Tabernacle, its crossbars, posts, bases, all its equipment, and everything related to their use.
Total number of Levites counted at Lord's command by Moses and Aaron, including every male a month old or more, was 22,000.
The number of the firstborn in Israelite are 22,273.
To redeem the 273 firstborn Israelites who exceed the number of the Levies, collect five shekels for each one, according to the sanctuary shekel which weigh twenty gerahs. It was 1,365 shekels.
The cebsus showed that the firstborn of Israel outnumbered the Levites by 273 and to redeem these a payment must be made.
Why?
All of the firstbron are belong to the Lord, so as all our first gain, include part time of our day is dedicating to the Lord. And my wage and earned are the grace of the Lord.
There was written error in total number, it seems 22,300, for the Kohath was 8600, may be was 8300, 3 and 6 are similar in Hebrew.
How?
Dear Lord, forgive me, for I did not devote part of my retire found to you. Please forgive me, I will do it now.