The number of God is three. The number of man is four.
God is the Trinity, three-in-one. I visualize this as:
God-Father <-> God-the-Spirit <-> God-the-Son
There is the person of Father, and the person of Son. The relationship between them is the expressed as the person of Spirit. Thus two entities, plus the relationship between them, equals three.
With man, created in the image of God, the two entities are Soul and Body, with the Mind being the expression of the relationship between the two. Then man has an additional relationship, with God, expressed as the Spirit.
God is timeless, existing simultaneously in all time, existing outside of time. But humans are mortal, existing in time. Mortals are in the image of God, operating in a world of three physical dimensions, plus time. Thus our number of dimensions equals our ‘number’ of four.
Perhaps our Spirit is the expression of timeless God into the physical world where time is a dimension: our Spirit is that line segment of linear time that is inhabited by our three-part human nature (soul-mind-body)?
Or here is another picture:
Timeless God is a sphere. Man-in-time is a line, infinite in only one dimension. The intersection of our line with the sphere of God can occur at only a single point. That point is our spirit.