The most fundamental and essential teaching in the Catholic faith

Catechism

The mystery of the Most Holy Trinity is the central mystery of Christian faith and life. It is the mystery of God in himself. It is therefore the source of all the other mysteries of faith, the light that enlightens them. It is the most fundamental and essential teaching in the "hierarchy of the truths of faith".   

"Now this is the Catholic faith: We worship one God in the Trinity and the Trinity in unity, without either confusing the persons or dividing the substance; for the person of the Father is one, the Son's is another, the Holy Spirit's another; but the Godhead of the Father, Son and Holy Spirit is one, their glory equal, their majesty coeternal" (Athanasian Creed: DS 75; ND 16).        

Do we worship the same mysterious God?

So the Father is God, the Son is God, and the Holy Ghost is God. And yet they are not Three Gods, but One God... And in this Trinity none is afore or after Other, None is greater or less than Another, but the whole Three Persons are Co-eternal together, and Co-equal.   Athanasian Creed NewAdvent (Catholic Encyclopedia)




There is one God: Father, Son, and Holy Spirit, a unity of three coeternal Persons. God is immortal, all-powerful, all-knowing, above all, and ever present. He is infinite and beyond human comprehension, yet known through His self-revelation. God, who is love, is forever worthy of worship, adoration, and service by the whole creation. (Gen. 1:26; Deut. 6:4; Isa. 6:8; Matt. 28:19; John 3:16 2 Cor. 1:21, 22; 13:14; Eph. 4:4-6; 1 Peter 1:2.)   Adventist.org