Rashi on Leviticus 18:2/רש"י על ויקרא י״ח:ב׳

1אני ה' אלהיכם I AM THE LORD YOUR GOD — I am He Who spoke on Mount Sinai “I am the Lord thy God" and Whose kingship you then accepted; now, therefore, accept My decrees! Rabbi Judah han-Nasi said: It was manifest and known to Him that in the days of Ezra they would ultimately revolt against restricting sexual relations, He therefore came to them with a decree emphasized by the words: "I am The Lord your God" — understand well Who it is that imposes this decree upon you, — the Judge (אלהיכם) Whose function it is to punish but Who is certain also to give a reward ('‎ה‎) (cf. Sifra, Acharei Mot, Section 8 1).