The Archdiocese of Detroit used the feast of the Most Holy Trinity, which refers to God, Jesus, and the Holy Spirit being three persons in one, to remind parishioners of the tie between the Trinity and the sign of the Cross.

“Happy Solemnity of the Most Holy Trinity!” the archdiocese said in a Facebook post. “Do you remember learning the Sign of the Cross? This simple gesture is one of our most basic prayers as Catholics, and proclaims the greatest mystery of faith: the Holy Trinity.” 

Pope Francis tweeted about the Trinity.

"The #MostHolyTrinity teaches us that a person can never be without the other," the pope said. "We are not islands, we are in the world to live in God’s image: open, in need of others and in need of helping others.” 

In another tweet, the pontiff said, "If we can truly invoke God, calling him ‘Abba — Dad,’ it is because the Holy Spirit dwells in us; he is the One who transforms us deep within and makes us experience the soul-stirring joy of being loved by God as his true children.” 

The mystery of the Holy Trinity is one of the basic tenets of the Catholic faith, which professes that there is only one God, but three divine persons: God the Father, God the Son, and God the Holy Spirit; a report from Catholic Culture said. God the Son, or Jesus, was begotten from the Father, and the Holy Spirit proceeds from both the Father and the Son. 

Catholics set aside time for the feast of the Holy Trinity, a celebration that dates to as early as the 10th century, on the Sunday after Pentecost Sunday; a report from Britannica said. 

“Today as you make the Sign of the Cross, ask the Lord to draw you close to the Trinity,” the archdiocese said.