“God is spirit, and those who worship Him must worship in spirit and truth.” (John 4:24)
Here Jesus teaches the Samaritan woman, and every one of us who reads the inspired record of her conversation with Him, something about God which is foundational to our understanding of Him, and how He must be worshiped:
“God is spirit”, Jesus said. He is not “physical”; He does not consist of created matter. He is spirit. Thus He is everywhere, like the air, or space. He is compared to “wind” in John 3 (and interestingly enough, the Greed word “pneuma” can mean either “spirit” or “wind”.)
The application? Because God is spirit, “those who worship Him must worship in spirit and in truth.” Because He is not “physical”, you don’t worship Him merely on a physical level. Material things alone will not placate Him. Because He is spirit, you worship Him in spirit. You must worship from your heart, with sincerity, with love, with adoration. Thoughtlessly going through the mere physical “mechanics” of worship activities will never be satisfactory to Him.
So that God is spirit is fundamental to our theology: our understanding of Who He IS.
And that God is spirit is also foundational to our understanding of how we must WORSHIP Him: “in spirit and truth.”