If we say that God is not material, it does not mean that He is necessarily spiritual.
He is neither one nor the other.
He is everything, just as He is never this or something else, never specifically spiritual or material, abstract or rational, never more of anyone aspect or less of another.
This is to imply that whatever we do know of the spiritual is still not enough to enable us to declare that it is of the same order of things as the Divine.
Our discernment is very limited.
Just as we do not see color beyond the infrared, or detect most electro-magnetic rays, which we measure but cannot really observe, most of reality remains in darkness as far as human perception is concerned.
–Rabbi Adin Steinsaltz
From The Candle of God by Rabbi Adin Steinsaltz