How can they make you their judge when they have the Torah, containing God's judgment; then they turn away after that. They do not acknowledge.
Translation endnotes
[5:42-43] This verse alone is an answer to those who consider Muhammed to be God's partner in legislation (hukm); the messenger was not a co-legislator (shari) of Islam. A group of Jews who sought Muhammed to judge among them was criticized for not referring to the Bible. The criticism, as it seems, had two reasons: Muhammed was not a legislator in the divine sense. Moreover, they should not jurisdiction-shop; they should stick with the laws they had agreed to apply in their community. It seems that no Muslim during the time of Muhammed demonstrated the ignorance of seeking Muhammed's judgment on matters expressed in the Quran. No wonder, 6:114; 98:5 and many other verses emphasize that the authority in Islamic system is God alone. However, when issues do not involve universal and absolute divine rules, muslims should refer to their elected officials and their appointees. Since Muhammed was the elected leader of the city-state of Yathrib, which had multiple jurisdictions accommodating a racially and religiously diverse population, he was in position to make judgments in daily affairs and the application of its secular Constitution. See 4:60. In brief, God alone has the power to legislate the universal laws of islam, and the leaders elected by muslims should follow those laws. They may issue laws, as long as they do not contradict universal laws issued by God, after consultation, and subject to change whenever the society wishes so. For Biblical verses on "laws," see Genesis 26:5; Exodus 16:28; 18:16,20; Leviticus 26:46; Ezra 7:25; Nehemiah 9:13-14; Esther 1:19; Psalms 105:45; Isaiah 24:5; Ezekiel 43:11; 44:5,24; Daniel 7:25; 9:10; Hebrews 8:10; 10:16.