The Trinity at Christ's Baptism
The word "Trinity" does not appear in the Bible. The idea behind the word is definitely biblical, though. The Trinity is, of course, the God of both testaments. The physical appearances of God in the NT (e.g. Jesus Christ, the Holy Spirit as a dove) is focused in the artwork dealing with the Trinity.
Baptism of Christ, The (1485-89):
Upper part of picture
Baptism of Christ, The (1505):
JUAN de Flandes
Baptism of Christ, The (C. 1508-19):
God the Father