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. AT: "the least important in his heavenly kingdom" or "the least important under the rule of our God in heaven" (See: [[rc://en/ta/man/translate/figs-metonymy]])
This can be stated in a positive form. AT: "that your righteousness must exceed ... in order to enter" (See: [[rc://en/ta/man/translate/figs-doublenegatives]])