“Pillar-of-the-world”? “Light-of-the-world”? God bless.
Heimdallr must be very old (he is said to be the father of all men) and must have enjoyed exceptional veneration:a particularly sacred character attaches to his face. He is the watchman of the gods and the guardian of the Bifrôst bridge; his senses are so keen that he hears the wool grow on the backs of sheep and sees the grass grow; in order to warn the gods of the coming of Ragnarok, he sounds the recall of his horn, Gjallarhorn.
One tradition made him a ram-god (as Thôrr would be a goat-god, Freyr a boar-god, Ôdinn a wolf-god or a horse-god, etc.), another, a personification of the Aurora - a notion of light presiding, in any case, over his character.
If we retain the etymology "pillar-of-the-world", it could be assimilated to the great cosmic tree Yggdrasill, also called Jôrmungandr (giant-magic-wand), which is another name of the great Serpent of Midgardr; its meaning would then be clearer:just as Midgardsormr keeps the world in place, “horizontally”, by enclosing it in the loop of its body, Heimdallr would ensure its “vertical” cohesion, according to the double cosmological representation. This image, satisfying for the mind, is far from exhausting all the possible interpretations of this enigmatic ase god.