In the Blessed Silence icon, Christ appears in the form of an angel. The depiction is closely associated with the Nativity (Christmas), after the prophecy of Isaiah:
"For a child is born to us, and a son is given to us, whose government is upon his shoulder: and his name is called the Messenger (Angel) of Great Counsel: for I will bring peace upon the princes, and health to him. His government shall be great, and of his peace there is no end." — Isaiah 9:6 (Septuagint)
Read more about this icon here.