This can be stated in active form. AT: "I am teaching people about the gospel of the kingdom of God" (See: [[rc://en/ta/man/translate/figs-activepassive]])
This contrast could be stated in the reverse order. AT: "even the smallest stroke of the letter of the law will last longer than heaven and earth will exist"
A "stroke" is the smallest part of a letter. It refers to something in the law that may seem to be insignificant. AT: "than for even the smallest detail of the law" (See: [[rc://en/ta/man/translate/figs-explicit]])