This can be stated in active form. Alternate translation: "if anyone ... teaches others to do so, God will call that person" (See: [[rc://en/ta/man/jit/figs-activepassive]])
The phrase "kingdom of heaven" refers to God's rule as king. This phrase is found only in Matthew. If possible use "heaven" in your translation. Alternate translation: "the least important in his heavenly kingdom" or "the least important under the rule of our God in heaven" (See: [[rc://en/ta/man/jit/figs-metonymy]])