The all seeing Eye

In the triangle, surrounded by a halo (French delta lumineux, English all-seeing eye), which shines in many boxes above the chair of the master, as a symbol taken from ecclesiastical customs, often plays a role in the master's degree of the freemasons, but above all in the systems that particularly emphasize the esoteric element. 

It is a symbol intended to remind people of the eternal watchfulness of God pervading all mysteries.

An eye in a triangle was placed over the crosses of the churches and over the high altars in the Middle Ages. This eye of providence is also found in the lodges of various systems, at the same time as a Masonic symbol.Dr. Mackey of his time (circa 1870) interpreted the "All-Seeing Eye" as a symbol of God's omniscience, and so had the support of the Masonic students of his generation.

The all-seeing eye may indicate divine omnipotence, but it can also symbolize one or more of the other five or six truths or ideas. 

It may also originally have stood for the sun as it rises at dawn - this interpretation was used by Shakespeare and many other writers.