From the beginning of creation in Genesis to the end of times in Revelation, God refers to Himself as "us" or "our" and thus describes the doctrine of the Trinity. The word trinity comes from "tri" meaning three and "unity" meaning one. God is three distinct individuals - God the Father, the Son Jesus, and the Holy Spirit - in one true God.
Let us rejoice that we have a Triune God who has provided for a Trinitarian salvation. When we were lost in sin, our God acted in every Person of his being to save us. The Father gave the Son, the Son offered himself on the Cross, and the Holy Spirit brought us to Jesus. We were so lost that it took every member of the Godhead to save us.
Dr Ray Pritchard
Within his own mysterious being God is Father, Son, and Holy Spirit. The designations are just ways in which God is God. Within the Godhead there are three "persons" who are neither three Gods nor three parts of God, but coequally and coeternally God. ....
Christian Theology in Plain Language, p. 143.
It is commonly said that the Trinity is a mystery. And it certainly is ... . But it is not a mystery veiled in darkness in which we can only grope and guess. It is a mystery in which we are given to understand that we will never know all there is of God ... . It is not a mystery that keeps us in the dark, but a mystery in which we are taken by the hand and gradually led into the light. ....
Eugene Peterson, Christ Plays in Ten Thousand Places
But simple as the Sign of the Cross is, it carries a brave weight: it names the Trinity, celebrates the Creator, and brings home all the power of faith to the brush of fingers on skin and bone and belly. So do we, sometimes well and sometimes ill, labour to bring home our belief in God's love to the stuff of our daily lives, the skin and bone of this world — and the Sign of the Cross helps us to remember that we have a Companion on the road.
Brian Doyle, Credo