In many icons of Nicholas, the Saint is shown flanked by Jesus Christ and the Mother of God either in medallions or, especially later, resting upon clouds. This is recalling a miracle from St Nicholas’ life.
At the First Council of Nicea (325 A.D.) the anti-Trinitarian heresy spouted by Arius so angered Nicholas that he walked over to Arius in mid-speech and struck him in the face. The scene is shown in all its glory in this fresco.
For his transgression, Nicholas was evicted from the Council, stripped of his bishorpic, and thrown in prison. Whilst there, Nicholas was visited one night by Jesus Christ and the Mother of God: Jesus holding a Gospel book, Mary a bishop’s stole. Christ handed the book to Nicholas, whilst the Theotokos offered the omophorion, restoring Nicholas to the rank of bishop, as it were, by Divine decree. The next morning the gaoler was astonished to find Nicholas miraculously unchained and dressed as a bishop. The First Ecumenical Council ultimately condemned Arius as a heretic, and St. Nicholas was indeed restored to the episcopacy. And so in icons of the Saint, Christ and St. Mary are shown giving the Gospel book and omophorion to Nicholas.
See also: “Bishop Nicholas Loses His Cool”, from St Nicholas Center