Since the Supreme Court can not make laws (that's the providence of congress) or enforce them (that's the providence of the executive), they can't really tell anyone what to do. All they can do is determine if a particular law does or does not fall into line with the underlying law of the land. And even that power is limited since any SC decision can be overturned "simply" by getting an amendment accepted.
By making the SC independent of mob rule (sorry, the "election process") and of party favor, it gives them a slim chance of doing what is right for the country. Unlike the administration which seems more concerned with what is right for its political party and congress which seems more concerned with pork.
When looking at the three federal branches, the SC was the one that Jefferson liked the least. Given the behavior of all three over time, I suspect that it would be the only one whose present existence he would support.