The palm tree as a symbol of Christ, or as the tree of life, was very popular in Ancient Christian Art. According to the beautiful hymn Vexilla Regis, the tree of life of the Christians is the cross of Christ.
The monogram (alpha and omega) indicates the divinity of Christ according to the Apocalypse, “I am the alpha and omega, the beginning and the end, saith the Lord God, Who is, and Who was, and Who is to come, the Almighty”.
