How can God be one God and three Persons?

This is the Trinity, one of Christianity's most central and historically settled doctrines, affirmed together by Catholic, Orthodox, and Protestant Christians alike, even though it remains genuinely difficult to fully picture or explain by analogy.

The historic, carefully worded formulation is this: God is one in being or essence, and three in person—Father, Son, and Holy Spirit are each fully God, not three gods, and not one God wearing three different masks at different times, but three distinct, eternally existing persons fully sharing in the one divine nature.

Common analogies—water existing as ice, liquid, and steam, or an egg's shell, yolk, and white—are popular but theologically inadequate, since they tend to describe either one thing appearing in different forms at different times, or one thing made of separate parts, neither of which captures three distinct, simultaneously existing persons sharing one undivided nature. Most theologians treat the Trinity as a genuine, revealed mystery to be affirmed rather than a puzzle analogies can fully resolve.