1 Samuel 16:
14But the Spirit of the LORD departed from Saul, and an evil spirit from the LORD troubled him.
1) What is the Spirit of Yahweh here? It is the Holy Spirit. The Holy Spirit is referred to in the Old Testament as the Spirit of Yahweh.
2) Where does the evil spirit come from? Does it come from satan? Does it do his will? No. It comes from God, and it does His will.
3) If the Spirit of Yahweh in the first part of the verse is supernatural, then why isn't the evil spirit in the second part of the verse supernatural? The answer to this is that the Spirit of Yahweh is demonstrably used in the Old Testament to refer to the Holy Spirit (this is verifiable), whereas the only previous use of the Hebrew phrase here translated 'evil spirit' is demonstrably a feeling of ill will between two parties. This is verifiable.