One of the hardest things to grasp about the nature of God is the idea of the Trinity. It is a stumbling block, especially for my Jewish friends who often ask me, “Doesn’t the Shema clearly say, Hear, O Israel! The LORD is our God, the LORD is ONE? Then how can God be one and three at the same time?”
I answer them with this question: What happens to sunlight when it passes through a prism? They usually know that it reaches our eyes as the colors of the spectrum, and so respond.
Then I ask if the red light is still light, and they answer that it is. Then I ask if the orange light is still light, and they answer that it is, and so on through yellow, green, blue, indigo, and violet. As we begin to discuss that example of white light passing through a prism to reveal itself as being composed of multiple colors of light, they begin to see that light can be perceived as the one color white or, if viewed after passing through a prism, as many colors, but that the resulting light is always light.
In like manner, the Holy Bible is the prism through which the God of Israel, when revealing himself to Moses, identified himself as One (Deuteronomy 6:4), but who has now in the fullness of time under the New Covenant chosen to identify himself in a more intimate way as God the Father, Son, and Holy Spirit.
My example is not a perfect explanation of the Trinity, since light itself is a created substance and the Father, Son, and Holy Spirit are not created beings but are instead the Creator, nor does it depend on the text of the Tanakh for the mental picture it paints, although 1 John 1:5 in the B’rit Hadashah does metaphorically say “God is light”.
Nevertheless, imperfect as it is, it does give a glimpse into the mystery of the triune nature of God that can be understood in everyday terms, showing that God can be perceived from a human viewpoint as a Tri-Unity without violating the Scripture that the Eternal God of Israel is One. — Dan Bruce