Dear friend, think about this, if I had only 2 dimensions as a flatlander, how could you introduce you to me as a 3 dimensional person? ( If I don't have the sense to perceive 3 dimensions, how can you make me understand that you have that extra dimension I don't have?) Well perhaps I could start to look at the shadows you project on the ground and wonder the mystery of you whose shapes change all the times and all a sudden your shadows disappear in the darkness too. I would wonder if you exist or not? What kind of a mysterious guy you are? ...etc. Even if I think so hard almost punching a hole in my brain I couldn't figure you out. Worst of all, if there is no light then I don’t think you exist at all.
I hope this analogy reminds you how tough for one to get into extra dimension he/she doesn't have, let alone spiritual dimension. For example, carps in the pond wouldn't understand our normal world beyond their watery world.
Actually if you could speak flatlanders’ language then you could describe yourself to them and your voice would make them aware of your existence, right? However, your self descriptions may still sound unbelievable to them. The best way seems that if you could become a flatlander yourself and speak their languages then there is possibility that they may come to know the true you. (well still partially since now you have stripped one dimension off yourself.) Nevertheless, it is still tough job for you to let flatlanders know the true you.
Somehow that explains the incarnation of Jesus-- He became a human being to reveal to us the invisible God. Do all these make sense to you now? It is hard for us to imagine 4th, 5th dimensions, not to mention infinite dimensions and spiritual dimension that only God can bring us into. That was why Jesus told an old intelligent man Nicodemus that he has to be born again( in spirit ) in order to see God's kingdom.
notes: After I wrote the above essay, I do come to realize my own blind spots in the analogy. Because if I were a flatlander, I probably wouldn't have eyes to see or ears to hear because all these organs are 3 dimensional. I was very limited to only able to think 3 dimensionally even when I was trying to imagine if I only had 2 dimensions. The flatlanders are doomed not able to figure out 3 dimensional world or persons. The best way is to add a 3rd dimension to the flatlander then he/she would simply understand the reality of 3 dimensional world. That is exactly what the Holy Spirit has done to open up a spiritual dimension for us to understand and see God's kingdom. ( If only one repents and believes in Jesus as his/her own personal Savior then the Holy Spirit will indwell in that person and restore his/her lost spiritual dimension.) Please excuse me, dear friend, after all an analogy is only an analogy, we couldn't push every details to match every part of the analogy or else it will certainly fall apart.
C.S. Lewis: A Short Introduction
By Philip Vander Elst
The analogy Lewis used to explain the Trinity was that of the cube:
On the human level one person is one being, and any two persons are two separate beings - just as, in two dimensions (say on a flat sheet of paper) one square is one-figure and any two squares we two separate figures. On the Divine level you still find personalities, but up there you find them combined in new ways which we, who do not live on that level cannot imagine. In God's dimension, so to speak, you find a being who is three Persons while remaining one Being, just as a cube is six squares while remaining one cube. Of course we cannot fully conceive a Being like that: just as, if we were so made that we perceived only two dimensions in space we could never properly imagine a cube. But we can get a sort of faint notion of it. (Mere Christianity, pp. 138-9)
...Thus we see that the Trinitarian conception of God is not some fantastic piece of gobbledegook dreamed up by the early Church, but a perfectly rational formulation about the Divine nature based on revelation (mainly but not solely through and in relation to Christ) but also appealing to reason, since it shows how God can be self-existent Love and therefore the source of human love. ( Philip Vander Elst)
…There is no good complaining that these statements are difficult. Christianity claims to be telling us about another world about something behind the world we can touch and hear and see. You may think the claim false; but if it were true, what it tells us would be bound to be difficult, - at least as difficult as modem Physics, and for the same reason... If Christianity was something we were making up, of course we could make it easier. But it is not. We cannot compete, in simplicity, with people who are inventing religion. How could we? We are dealing with Fact. Of course anyone can be simple if he has no facts to bother about. (Mere Christianity, p.134)