I would contend that to truly understand the meaning of ONE is to truly understand the meaning of GOD.
For me, it required a series of deep contemplations that ended up in absolute understanding. Absolute understanding of the meaning of ONE.
ONE means EVERYTHING. Every bit of substance, essence, feeling, response, concept. TRUTH. A fully locked reasoning. Fully controlled. Fully realized. Perfection. Lacking nothing. ALMIGHTY.
Contemplate this concept first. This is before Creation.
An ALMIGHTY ONE that, in His Perfection, before the beginning of anything we can contemplate, made Himself eternally alive. Eternally alive so that you are contemplating this even now.
An ALMIGHTY ONE who made Himself . . . into THREE.
ONE Made an eternal sacrifice. Begetting a Second Person equal to Him in His Substance, He risked His eternal harmony. The Second Person - understanding ONE's sacrifice - turned to ONE and Eternally Sacrificed in return, giving up His Own Divine Will to Do only the Will of ONE. Becoming a Sacrificing Son to an Almighty Father.
This Eternal Sacrifice is "Love". Brand new. Something beyond EVERYTHING. This Love that transcends EVERTHING is contained in the Third Person, the HOLY SPIRIT.
The HOLY SPIRIT - EVERYTHING plus LOVE - given to us that we may discern the Will of Our Creator.
We are made in His Image. Our modern minds eat freely from the tree of good and evil. Knowing evil, we may become comfortable in it.
The HOLY SPIRIT - THREE - led to the creation of man who honors the Father with multitudes of children.