If you are challenged to explain the Trinity, consider this. From all eternity, before material creation and time, God desired a communion of love. He therefore expressed Himself in a perfect Word. The Word God uttered beyond and outside of time was and remains His perfect self-expression, containing all that God is, perfectly possessing every characteristic of the Speaker: omniscience, omnipotence, truth, beauty and personhood. Thus, from all eternity there were always, in perfect unity, the God who spoke and the Word who was spoken, true God with and from true God, Begetter and Begotten, distinct Father and distinct Son having the same indivisible divine nature.
This was never not so. Eternally these two Persons contemplate each other. Hence, they knew and loved each other such that each offered the other a perfect gift of self-giving. This mutual self-gift by these perfect and distinct divine Persons, containing all that each one is, is necessarily perfectly given and perfectly received. Therefore, the Gift between Father and Son also contains all that each have: omniscience, omnipotence, truth, beauty and personhood. Consequently, from all eternity there are three divine Persons having one indivisible divine nature, God the Father, God the Son, and the perfect mutual self-gift of love between them, God the Holy Spirit.
This is the foundational saving doctrine we believe as Christians and which we celebrate on Trinity Sunday. At the core of everything else we believe in and hope for, we will find this mysterious doctrine of divine relationship, the Triune God: the One and Three God in whose image and likeness we are made.
The communion of Persons in the Trinity is written into our beings as images of God. Our dealings with others ought to reflect the communion we were created for in God’s loving plan.
Speaking of harmony with this foundational mystery of our faith and identity, St Hilary of Poitiers (d 368) prayed: “Keep, I pray, uncontaminated this upright faith that is in me and, until my last breath, and grant me likewise this voice of my conscience, that I may be ever faithful to what I professed in my regeneration when I was baptised in the name of the Father, and of the Son, and of the Holy Spirit” (De trinitate 12, 57).
We must strive with grace and elbow-grease to give the Trinity glory in all that we do, think and say.