Sun-worship played a prominent part in the religion of the ancients and was introduced into the mysteries, says [Bro. Albert] Mackey, not as a material idolatry, but as a means of expressing an idea of restoration to life from death, drawn from the daily reappearance in the East of the solar orb after its nightly disappearance in the West. The Gnostics derived many of their symbols from the Mithraic initiations, in which sun-worship played an important part. These again exercised their influence upon the medieval Freemasons. Thus it is that the sun has become so prominent in the Masonic system; not as an object of worship, but purely as a symbol, the interpretation of which is presented in many different ways. As the source of material light the sun reminds the Mason of that intellectual light of which he is in constant search. But it is especially as the ruler of the day, giving to it a beginning and end, and a regular course of hours, that the sun is presented as a Masonic symbol. Hence, of the three lesser lights, we are told that one represents or symbolizes the sun, one the moon, and one the Master of the lodge, because as the sun rules the day and the moon governs the night, so should the Worshipful Master rule and govern his lodge with equal regularity. And this is in strict analogy with other Masonic symbolism. For if the lodge is a symbol of the world, which is thus governed in its changes of times and seasons by the sun, it is evident that the Master who governs the lodge, controlling its time of opening and closing, and the work which it should do, must be symbolized by the sun.
[Bro. Wildey E. Atchison, “The Symbolic Lights,” The Builder, September, Vol. IV, №9, 1918, 269–70.]