Question: "What does it mean that God is spirit?"
Answer: The teaching that “God is spirit” is found in John 4:24: “God is spirit, and his worshipers must worship in the Spirit and in truth.” Jesus said this to a woman who thought that physical locale has a bearing on proper worship of God.
The fact that God is spirit means that God the Father does not have a human body. God the Son came to earth in human form (John 1:1), but God the Father did not. Jesus is unique as Emmanuel, “God with us” (Matthew 1:23). Numbers 23:19 emphasizes God’s truthfulness by contrasting Him with mortal men: “God is not human, that he should lie, not a human being, that he should change his mind.”
Some question why the Bible sometimes speaks of God as if He has a body. For example, Isaiah 59:1 mentions God’s “hand” and “ear.” Second Chronicles 16:9 speaks of God’s “eyes.” Matthew 4:4 puts words in God’s “mouth.” In Deuteronomy 33:27 God has “arms.” All of these verses are examples of anthropomorphism—a way of describing God with anatomical or emotional terms so that humans can better understand Him. The use of anthropomorphism, a form of figurative language, does not imply that God has an actual body.
To say that God is spirit is to say that God the Father is invisible. Colossians 1:15 calls God the “invisible God.” First Timothy 1:17 praises God, saying, “To the King of the ages, immortal, invisible, the only God, be honor and glory forever and ever.”
Even though God is spirit, He is also a living, personal being. As such, we can know Him personally. Joshua 3:10 speaks of God in this way, saying, “You will know that the living God is among you.” Psalm 84:2 declares, “My heart and flesh sing for joy to the living God” (ESV).
Philosophically, God must be a spirit in order to be infinite. Also, if God was limited to a physical body, He could not be omnipresent (in all places at once). God the Father is not limited to the dimensional restrictions of created things but can exist in all places at one time. God is the uncreated First Cause that is the power behind all other beings.
Interestingly, in John 4:24 Jesus makes the connection between God being spirit and worshiping Him in spirit and in truth. The idea is that, since God is spirit, people must worship Him accurately (in truth) and in spirit (with their soul or heart), as opposed to relying on traditions, rituals, and physical locales.