And I will also take of them for priests and for Levites, saith the LORD. – Isaiah 66:21

Observe, according to the text, men have nothing to do with the selection; for here it is said, “I will also take of them”—not “their parents shall bring them up to it;” not “those who shall be looked out as the most fit and proper men on account of some natural bent and bias, or gift and talent, but I will take.” God’s priesthood in the world is a priesthood of His own choosing, of His own setting apart, of His own anointing. “He hath made us kings and priests unto God.” The church is a royal priesthood, not of man, neither by man, nor of the will of man, nor of blood, nor of birth: it is of God’s choosing. This sacred and consecrated band of priests and Levites, and all that serve God effectually and acceptably, are men whom He has Himself chosen to the work. He Himself hath done it, and only His own will has been consulted in the matter. In their case, it appears from the text, that whatever was unfit in their character has been overcome by divine grace. “I will also take of them for priests and for Levites, saith the Lord.” If God takes them for Levites, He makes them Levites; if He chooses them for priests, He makes them priests. So, glory be to His name, when He chose you, my dear brother, when He chose you, my dear sister, to be His servants, to be His priests and His Levites, He gave you the grace you wanted. He found in you no natural fitness, no suitability, but in fitness for sin, a suitability to go astray, and to become a brand for the burning; but if there be a fitness in you to serve Him on earth and in heaven, it is His grace that has done it. It is His grace speaking in all its wondrous majesty—”I will take of them for priests and for Levites”—which has effected in you the great transformation, making in you all things new, and thus qualifying you to become the servants of the Most High. ~ C.H. Spurgeon

https://www.blueletterbible.org/comm/spurgeon_charles/sermons/0992.cfm