On Sunday the Archdiocese of Milwaukee celebrated the feast of the Holy Trinity, which refers to the concept of God, Jesus and the Holy Spirit being three persons in one.

“Every time that we make the sign of the cross, we draw closer to the great mystery of the Trinity,” Pope Francis was quoted as saying of the event on the archdiocese’s Facebook page. The archdiocese added that the Sunday Mass was designed to help the faithful “‘draw closer’ to the Father, Son, and Holy Spirit."

Catholics traditionally celebrate the feast of the Holy Trinity on the Sunday after Pentecost Sunday. Britannica traces the roots of the event to as early as the 10th century. 

The mystery of the Holy Trinity is a fundamental aspect of the Catholic faith, which teaches 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. 

"The #MostHolyTrinity teaches us that a person can never be without the other," Pope Francis said in a tweet. "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 a separate tweet, the pope 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.”