The word דבר (speak) indicates an expansion of matters in a way of interpreting, lengthening, and expanding one’s words. Thus, with this it indicates what God spoke with Moses mouth to mouth, namely the teaching of the Oral Law and the specifics of the laws at length. And באמירה (saying/expression) indicates the Written Law according to the language in which it was spoken to Moses.

And according to this, it includes proselytes from ואמרת אליהם (and say to them)⁶²⁸, through what I explained at length.

Leviticus 15:2 says,דברו אל בני ישראל ואמרתם אלהם איש איש כי יהיה זב מבשרו זובו טמא הוא(Speak to the children of Israel, and say to them: When any man has an issue out of his flesh, his issue is unclean), using the language דברו אל בני ישראל ואמרתם אליהם for “Speak to the children of Israel, and say to them”. The extra words ואמרתם אליהם (and say to them) are there to include proselytes⁶²⁹.

footnotes: ⁶²⁸ Leviticus 15:2. ⁶²⁹ Malbim, HaTorah v’HaMitzvah Metzora 119.