The word Trinity does not occur in the Bible. The term was coined by people who wanted a word to express the idea that there was one God, a single unity revealed to humankind in three aspects. For reasons embedded in the Greek language of the time, these aspects are referred to as Persons, and they comprise one Being. These co-eternal Persons are traditionally identified as Father, Son, and Spirit. The role of Creator is ascribed to the Father, the role of Redeemer to the Son, and the role of Sustainer to the Spirit. And, yet the three make up just one God.
It's all very complicated.
The need to explain complicated things occurs in many different fields, and one device often used is that of analogy. Robert Burns, the eighteenth century poet, famously tried to explain love by means of analogy: "O my love is like a red, red rose that's newly sprung in June. O my love is like the melody that's sweetly played in tune." He didn't mean that love emitted electromagnetic radiation at a specific wavelength, that it sprouted in only one month of the year, or that it required the transmission of precise sound vibrations. Instead, his words evoke aspects of love, elements such as vibrancy, purity, tenderness, longing, harmony, and perfection.
Physics is another arena where analogy is often used to help explain complex concepts. For example, Albert Einstein described gravity as a warping of spacetime. Teachers often explain the idea by way of an analogy involving a bowling ball on a tautly stretched rubber sheet. The heavy object creates an indent analogous to the curvature of spacetime. Rolling a marble at various speeds across the indentation shows different ways in which an object moving in a straight line is deflected in a curved environment. Many students have watched such demonstrations and experienced an "ah-ha" moment of understanding; for them, the analogy is successful. Others just scratch their heads. If gravity is merely a warping of spacetime, they wonder, what causes the bowling ball to deform the sheet in the first place? Rather than gaining cosmological insight, these students discover that the analogy isn't perfect.
When it comes to explaining the triune nature of God, many people have also undertaken the task of providing analogies. Some talk about eggs (yolk, whites, and shells); others talk about men (who may be sons, brothers, and fathers). Some prefer to consider water, which may exist in different states: a gas, a liquid, or a solid. Because these analogies are repeated so often, I presume they must help some people experience insight. I have never found myself among them. To my mind, these analogies speak about a divided, ever-changing God. They leave me scratching my head.
I'd like to propose a different analogy. It isn't perfect either, and if it leaves you confused, just set it aside. (Better yet, use the comments section below to suggest another.)
The triune nature of God can be likened to a sphere.
A sphere is the three-dimensional version of a circle, comprising all of the points in space that fall within a boundary equidistant from a central point. To define a specific sphere, one must identify its middle and specify the radius.
You've probably seen countless examples of spheres represented by objects of different sizes and materials (ball bearings, marbles, beach balls, etc.). To see objects such as these, you rely on their boundaries, the surfaces they present to the world. Mathematically, these surfaces can be described as a border formed from the end points of an infinite number radii emanating from the center. And, for a sphere's structure to hold together, it must be made out of something. Metal. Glass. Plastic. Something.
So, how is the Trinity like a sphere? The Father, the Creator, is like the mathematic principles that identify the central point and measure the radius. These are analogous to the principles that describe and define God. Jesus, the Son and Redeemer, is like the visible surface. It is the part of God that presents God's self to humanity and through which people try to see more of the interior of God. The Spirit, the Sustainer, is like the substance out of which God is made.
Three in one, co-existing. In this spherical analogy, each part can be envisioned as the entire sphere. The center point and radius define and create the sphere. The surface generates the sphere. The material produces the sphere. Take any one of these concepts individually—the mathematics, the boundary, or the substance—and you've still got a sphere. And, yet, each is different. Each serves a unique purpose.
This analogy isn't perfect. It might create a misperception that God is somehow measurable with a yardstick or that God might roll downhill if you lose your grip. It also doesn't help with trying to figure out whether we're inside God or God is inside us. Nevertheless, it helps me envision how three differently described entities can actually be a complete, undivided whole One.