""God is a Spirit" (or, more accurately translated, "God is Spirit"), declares the Scripture (John iv. 24), "and they that worship Him must worship Him in spirit and in truth."What does it mean to "deny matter"? From a Christian Science perspective, Spirit is one thing and matter is another thing completely. But such a perspective posits two ultimates: Spirit (or God) and matter (or not-Spirit). However, Spirit is Infinite and All, thus precluding the existence of anything not Spirit. If Spirit is All, one has at least two possible implications: (1) matter, as non-Spirit, doesn't exist; or (2) matter, apparently non-Spirit, is actually Spirit, perhaps Spirit in a different form (since Spirit is Infinite, Spirit could manifest in Infinite number of forms, including matter). Christian Science takes the first implication, but the second implication is more consistent with both reason and experience.
If God is Spirit, and God is All, surely there can be no matter, for the divine All must be Spirit....
Hence my conscientious position, in the denial of matter, rests on the fact that matter usurps the authority of God, Spirit; and the nature and character of matter, the antipode of Spirit, include all that denies and defies Spirit, in quantity or quality."
-- Mary Baker Eddy. Unity of Good. Boston: The First Church of Christ, Scientist. 1908. 31; in Mary Baker Eddy. Prose Works Other Than Science and Health with Key to the Scriptures. Boston: The First Church of Christ, Scientist. 1925.
There is one way that the Christian Science perspective may be accurate, and that way involves defining matter not as a form of being, but as a psychological dynamic. If matter is the assumption that something non-Spirit does in fact exist, then matter could reasonably be rejected and denied. In other words, the problem is not that what we call matter exists; the problem is in mentally presuming that what we call matter is separate from Spirit, not-God.