Why is this even necessary? A law or ruling either follows the constitution, or doesn’t, in which case it is invalid.
It really isn't but it looks good to the voters.
Exactly right. That seems to me to be a core question.
Although it would seem appropriate for a court to recognize Sharia law if such is an express term in a contract between private parties, such term has no bearing on other parties. To allow a religious law to somehow gain a foothold as a "common commercial practice" and thus applicable to all is, at the least, an affront to the local legislature.
Why is this even necessary? A law or ruling either follows the constitution, or doesn’t, in which case it is invalid.
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Because we have rats in the Supreme Court that entertain foreign law in their decisions. They should be impeached.