Hermano, I appreciate what you wrote about God not commanding that people be killed. I am in basic agreement with your explanation.
Yes, it APPEARS that Jesus is saying that Moses’ words are the commandment of God. But He may have been saying, “God said…” because the Jews BELIEVED that God had said what Moses stated that He had said. And so Jesus then showed that the Jews weren’t really carrying out the commands that “God gave them” (according to Moses).
Let me give you a more recent example in Islam:
27 ¶ O ye Children of Adam! Let not Satan seduce you, in the same manner as he got your parents out of the Garden, stripping them of their raiment, to expose their shame: For he and his tribe watch you from a position where ye cannot see them: We made the Evil Ones friends only to those without Faith.
28 When they do aught that is shameful, they say: “We found our fathers doing so”; and “Allah commanded us thus:” Say: “Nay, Allah never commands what is shameful: Do ye say of Allah what ye know not?”
29 Say: “My Lord hath commanded justice; and that ye set your whole selves to Him at every time and place of prayer, and call upon Him, making your devotion sincere as in His sight: Such as He created you in the beginning, so shall ye return.” (Koran 7)
From verse 24, these words are quoted as the words of Allah. “Allah” is simply the Arabic word for “God.” When a Muslim who speaks Arabic becomes as Christian, he continues to address God as “Allah,” for that is the word “God” in his language.
A Christian missionary to the Muslims might say to them, “As Mohammed wrote, God said that He commands justice and never commands what is shameful,” but YOU say, “It is just and not shameful for us to rape non-Muslim women in the name of God—thus you make the commandment of God of no effect!” This doesn’t imply that the missionary believes that God actually said those words, but since Muslims BELIEVE He said them, the missionary talks to them as if He had said them. I think Jesus was doing the same thing with the Jews.