Jesus said this beside a well
Jesus spoke about God being spirit while talking with a Samaritan woman at Jacob's well. She raised an old dispute between Samaritans and Jews: was the right place to worship on Mount Gerizim or in Jerusalem? Jesus pointed beyond the argument. A time was coming when true worship would not be tied to either mountain (John 4:20-23).
God is not a creature who occupies a body as we do, nor can he be kept inside a shrine, nation or church building. When Solomon dedicated the temple in Jerusalem, he marvelled that even heaven could not contain God, let alone the temple he had built (1 Kings 8:27). So you do not need to reach a special location before God can hear your prayer.
God is a Spirit: and they that worship him must worship him in spirit and in truth.
Not a vague force
Calling God spirit does not make him less personal. In the same conversation, Jesus calls God Father and says that the Father seeks true worshippers (John 4:23). God knows, loves, speaks, wills and acts. He is not an energy we learn to control.
The Bible calls him the eternal and invisible King (1 Timothy 1:17). Invisible does not mean absent. David reflected that no height, depth, or distant sea could place him beyond God's presence (Psalms 139:7-10). That can bring comfort when life feels lonely, confusing or hidden.
Now unto the King eternal, immortal, invisible, the only wise God, be honour and glory for ever and ever. Amen.
God has shown us who he is
We cannot see God in his fullness by our own effort, but he has not left us guessing. Jesus reveals the Father (John 1:18). As you watch Jesus welcome outsiders, confront evil, forgive sinners and give himself in love, you see what God is like.
Christians also confess that the Holy Spirit is God, not merely a helpful influence. Jesus promised that the Spirit would lead his disciples into truth and bring honour to him (John 16:13-14). Knowing the unseen God is therefore not just collecting religious ideas. It is responding to the Father made known through the Son, with the help of the Holy Spirit.
No man hath seen God at any time; the only begotten Son, which is in the bosom of the Father, he hath declared him.
Worship in spirit and truth
Jesus connects God's spiritual nature with worship in spirit and truth (John 4:23-24). This is not mainly about a certain musical style, emotional mood or private setting. It means coming to God sincerely, relying on his Spirit, and worshipping the God who has truly revealed himself rather than an invented version that suits us.
That can happen in a church gathering, at a kitchen table, on a bus, or during a difficult night when words are hard to find. God is not trapped in a building, and he is not impressed by polished language. Come honestly. Reading the conversation in John 4:20-24 can help you see how kindly Jesus invited this woman into a deeper knowledge of God.