The central angel in Rublev’s Icon represents Christ. The visitors to Abraham narrative in Genesis 18, was long regarded as a theophany of Jesus. The LXX renders Genesis 18.1 as, θεὸς (God) appearing to Abraham, while the Masoretic text has 'YHWH appeared' to Abraham. This angel typically appeared in Icons prior to Rublev with the inscription IC XC (Jesus Christ) in his nimbus. Rublev leaves out the Christological inscription but adds symbol and colour to identify this person as Christ.
Firstly we notice the different colours of the angel’s robes. His Chiton is dark purple, decorated with a golden clavus (stripe). His chlamys is of a deep azure-blue. These colours are important. The angel on the left, representing the Father, wears a blue chiton, which is almost entirely hidden, while the central angel wears blue as his prevailing colour. The difference points to the theological idea that the Father is invisible, while the Son has revealed Him to us. Even in his humanity, Jesus has revealed to us the ‘glory’ which He possessed as the Son of God, And the Word became flesh and dwelt among us, and we have seen his glory, glory as of the only Son from the Father, full of grace and truth (Jn. 1.14). God the Father is seen through His unique Son, Philip said to him, "Lord, show us the Father, and it is enough for us." Jesus said to him, "Have I been with you so long, and you still do not know me, Philip? Whoever has seen me has seen the Father. How can you say, 'Show us the Father'? (Jn. 14.8-9)
The angel’s right arm is free, and with it He points to (and blesses) the chalice on the table which contains a calf’s head. The calf’s head is a reminder of the hospitality of Abraham (Gen 18.7); the chalice however is a clear symbol of the Eucharist, the sacrifice of Christ, and the axis of a wordless divine conversation. The angel’s hand gesture goes beyond the chalice and points to the angel on the right, who represents the Holy Spirit. The original Icon had the central angel simply point with his index finger (which is more directly pointing towards to the Holy Spirit) but later painters added the middle finger and adapted the gesture to form the sign of a blessing.
The head and the gaze of the angel are directed towards the angel on the left. This was a departure from earlier Icons which normally portrayed the central angel gazing towards the viewer. The Son now looks to the Father. This adaptation by Rublev, subtlety shifts the centre of gravity to the angel on the left. The gestures of all three angels allow us to view them in communion with each other.
Behind the central figure is a tree. Again it echoes the Genesis account where Abraham entreats the strangers to; rest yourselves under the tree (Gen. 18.4). It is also a symbol for the victory of Christ on the cross at Calvary, He himself bore our sins in his body on the tree, that we might die to sin and live to righteousness. By his wounds you have been healed (1 Pet. 2.24).
Ultimately, it is because of Christ’s victory at Golgotha, the place of the skull, that we, strangers, aliens, even enemies of God, can be brought into the fellowship of divine mystery. We take the cup of thanksgiving and remember that the Triune God invites us to rest under the tree. The tree being the blood stained cross of Christ.