Question: What is the meaning of Deuteronomy 18:9-22 for necromancers?
These are warnings (to be taken seriously, on pain of death), initially to the Jews of the time, but now for all potential necromancers, because the warnings ignored are tantamount to Satan worship!
First, it is important to read and absorb the context of the verses you quote!
This applies to all of Scripture, as there is an increasing tendency to take Words out of context for the wrong reason in many Bible Groups!
18:1–8 deals with the apportionment of various items to Priests and Levites.
Vs. 9–14, warns against the adoption of the customs of the conquered peoples!
Vs. 15–22, gives the prophecy of Christ Jesus, the genuine prophet, and the false prophet; and the warning that to not hear the genuine prophet (Jesus etc.) will lead to God’s judgment of those people!!