In Euclidian Geometry - "the triangle - is the first polygon to enclose space."  Both in terms of "geometry" itself and "metaphysically" - the triangle therefore assumes a special significance among the polygons. 

 

Being the "first polygon which encloses space" - singularly marks the triangle out and by "extension" - "all things three." 

 

Euclidian Geometry can be regarded - as the "hardware of the mind, in its enclosing of space, as do all polygonic forms.  Space itself, can be regarded as an expression of the Infinite.  Hence, the significance of the abstract concept - "of an enclosed Infinite"" (Oladipo Adegboyega Adelaja, SOTI Collected Works - "Geometrical Forms & Metaphysics.") 

 

The circle is also - a singularly and esoterically geometric form.  It encloses the 'Infinite,' however - the circle, being the 'One' - stands alone.

 

The significance of the triangle and the concept of "three-ness," which is an attribute of the triangle - "is expressed in the sacred idea of "The Trinity."  In Christianity, this is expressed through the concept of The Father, The Son and The Holy Spirit.  Other religions also express this concept of the trinity - it is found in Hinduism (Brahma, Vishnu, Shiva.)

 

"The significance of "three-ness" - is not only found in the concept of "The Trinity" - but also in "Sacred Geometry" generally" (Oladipo Adegboyega Adelaja, SOTI Collected Works - The Science Of Abstract Consciousness -"Sacred Geometry, Religion & Spirituality") - this finds expression, in the triangular form and is known as "The Three Attributes of Consciousness."  ​