Protestant
Where is the Trinity in the Bible?
The word 'Trinity' never appears, but the reality is woven throughout Scripture: one God who is Father, Son, and Holy Spirit, each fully divine, distinct, yet one in being — most explicitly at Christ's baptism and the great commission.
Catholic teaching
The Church did not invent the Trinity at Nicaea; it articulated in precise philosophical terms what the apostolic faith already confessed from the New Testament data — one divine nature subsisting in three distinct Persons, a mystery beyond reason but not against it.
Biblical foundation
At Jesus' baptism the Father speaks, the Son is baptized, and the Spirit descends as a dove (Matt 3:16-17). Christ commands baptism 'in the name of the Father and of the Son and of the Holy Spirit' — singular 'name' for three Persons (Matt 28:19). Paul's benediction names all three as co-equal sources of grace (2 Cor 13:14), and John opens his Gospel declaring the Word was God and was with God (John 1:1).
Scripture references
Historical evidence
Before Nicaea (325), Tertullian had already coined the Latin term 'Trinitas' around AD 213, showing the doctrine was recognized and named nearly a century before the council merely defended it against Arian denial.
The Church Fathers
“All are of One, by unity of substance; while the mystery of the dispensation is still guarded, which distributes the Unity into a Trinity, placing in their order the three Persons.”