Ever seen the Holy Ghost? He can be tricky to substantiate (pun intended), but is in fact more real than matter.
According to John, Jesus spoke the following words to his disciples at the Last Supper:
Ἐὰν ἀγαπᾶτέ με, τὰς ἐντολὰς τὰς ἐμὰς τηρήσετε: κἀγὼ ἐρωτήσω τὸν πατέρα καὶ ἄλλον παράκλητον δώσει ὑμῖν ἵνα μεθ’ ὑμῶν εἰς τὸν αἰῶνα ᾖ, τὸ πνεῦμα τῆς ἀληθείας, ὃ ὁ κόσμος οὐ δύναται λαβεῖν, ὅτι οὐ θεωρεῖ αὐτὸ οὐδὲ γινώσκει: ὑμεῖς γινώσκετε αὐτό, ὅτι παρ’ ὑμῖν μένει καὶ ἐν ὑμῖν ἔσται.
~John 14:15-17, OGB
An English translation, drawn from the NIV (and a tad bit of Ancient Greek):
If you love me, you will obey my commands; and I will beseech the Father, and he will give you another counselor to be with you forever: the Spirit of Truth, whom the world cannot accept because it neither sees him nor knows him. But you know him, for he stays beside you and will be in you.
Hovering around chapters 14 and 15, Jesus speaks more about this “Spirit of Truth” …
- The counselor – the Holy Spirit – whom the Father will send in my name, will teach you all things and will remind you of everything I have said to you.
- The counselor – the Spirit of Truth – will testify about me, and you also must testify. He comes from the Father, and I will send him to you.
- The Spirit of Truth will guide you into all truth.
The Spirit of Truth is like your conscience, or moral intuition, yet he is more than that. He is the channel through which the Living Water flows into you. The closer you are to the Source of Life, the better you know right from wrong. The further you stray from the Fountain, the more confusing morality becomes, til you become altogether blind to truth.
C.S. Lewis explains the relationship between Father, Son, Holy Spirit, and man in his book, Mere Christianity:
The Father delights in his Son; the Son looks up to his Father… They are a great fountain of energy spurting up at the very center of reality. If you are close to it, the spray will wet you; if you are not, you will remain dry… Christ is the Son of God. If we share in this kind of life we shall also be sons of God. We shall love the Father as he does and the Holy Ghost will arise in us.
A final piece of imagery. Jesus’ words, from chapter 15 of John:
I am the true vine, and my Father is the gardener. He cuts off every branch in me that produces no fruit and cleanses every branch that does produce fruit to make it even more fruitful. Remain in me, and I will remain in you. No branch can produce fruit by itself; it must remain in the vine. Neither can you produce fruit unless you remain in me. I am the vine; you are the branches. If a man remains in me and I in him, he will produce much fruit; apart from me you can do nothing. You did not choose me, but I chose you and appointed you that you might set out and produce fruit – imperishable fruit.