In the context of being accused of blasphemy (on the grounds that he, a human being, had claimed to be God’s son) Jesus talks in John 10:22–42 about the nature of his relationship with God.
Although the word ‘Trinity’ does not occur in the Bible, significant New Testament references to the Father, Son, and Holy Spirit (cf. Matthew 28:18–20; 2 Cor 13:14, as well as this passage from John) gave rise to a Trinitarian notion of the divine—God is one, undivided and immutable in substance and yet lives and acts in the three persons of Father, Son, and Holy Spirit.
Once the Christian faith had become the accepted religion of the Roman Empire under Constantine in the early fourth century, and Christian art and architecture began to flourish, visual artists began to grapple in earnest with this complex dogma.
This English sixteenth-century illumination is one of the most unusual, imaginative, and striking in the wide range of Trinitarian images in the history of Christian art. While the triandric iconography (three male figures of identical appearance) was to develop as a type of Trinitarian iconography around the twelfth century, this composition is unique in its superimposition of the sun, its rays both covering and emanating from the Trinity, and pervading the whole page. While Father and Son look almost identical, so as to underscore their oneness and unity, the Holy Spirit’s body is rendered in white as a youthful figure, not uncommon in Trinitarian iconography—a pictorial attempt, it seems, to render the non-corporeal pure, dynamic, ever-alive nature of the Spirit.
The divine light both is and springs from God and shines into the world with multiple tiny angels in red, like flames, and in white, like doves—references to the Holy Spirit and to divine love. The symbols of the four Evangelists are included in each corner. The illumination thus alludes to the one God, the creator God, to God as light of the world, to divine, kingly omnipotence (the crown), as well as to the proclamation of the good news (Evangelists) and thus indirectly to the divinely-inspired church on earth.
http://www.bl.uk/catalogues/illuminatedmanuscripts/record.asp?MSID=8712&CollID=16&NStart=20215 [accessed 14 July 2018]
Thiessen, Gesa Elsbeth. 2009. ‘Images of the Trinity in Visual Art’, in Trinity and Salvation: Theological, Spiritual and Aesthetic Perspectives, ed. by Declan Marmion and Gesa Elsbeth Thiessen (Oxford: Peter Lang), pp. 119–40