Mark 12.28-29: “One of the scribes came near and heard them disputing with one another, and seeing that he answered them well, he asked him, “Which commandment is the first of all?” Jesus answered, “The first is, ‘Hear, O Israel: the Lord our God, the Lord is one…”

…in other words, Jesus declares that the Shema Yisrael, the most basic of all Jewish prayers, is one of two greatest commandments. (Somehow Christians tend to forget the Jewish origins of this prayer.)