Numbers 8:26
But shall minister with their brethren in the tabernacle of the congregation, to keep the charge, and shall do no service. Thus shalt thou do unto the Levites touching their charge. But shall minister with their brethren in the tabernacle of the congregation, to keep the charge, and shall do no service. Thus shalt thou do unto the Levites touching their charge.
At fifty years old the Levites were released from arduous and strenuous service. They were not discharged but continued to minister with their brethren in the tabernacle to keep the charge, assisting them without performing the demanding duties. This sanctuary work, carried on largely in the court, is a type of the gospel ministry. Old age may therefore end active labor in God's service without ending the duty and privilege of waiting on God.
The law of Moses makes provision for those who have officially served the Lord fifty years, showing that God pensions His old servants as a humane government pensions its old soldiers. God never leaves His people because they are old if they have continued faithfully in His service. A man does not cease to be a priest when he gets old and does not cease to be a minister of the gospel when he gets old. The tithe is the proper fund to care for the Lord's ministry, so aged laborers who can no longer do active ministerial work remain ministers and should be supported from the tithe.