That Gayatri (as described before with its three feet) rests on that fourth foot, the bright one, high above the sky. And that again rests on the True (satyam), and the True is the eye, for the eye is (known to be) true. And therefore even now, if two persons come disputing, the one saying, I saw, the other, I heard, then we should trust the one who says, I saw. And the True again rests on force (balam), and force is life (prana), and that (the True) rests on life. Therefore they say, force is stronger than the True. Thus does that Gayatri rest with respect to the self (as life). That Gayatri protects (tatre) the vital breaths (gayas); the gayas are the pranas (vital breaths), and it protects them. And because it protects (tatre) the vital breaths (gayas), therefore it is called Gayatri. And that Savitri verse which the teacher teaches, that is it (the life, the prana, and indirectly the Gayatri); and whomsoever he teaches, he protects his vital breaths.

In plain words: The Gayatri rests on its shining fourth part, which rests on truth, and truth is the eye, which is why we trust someone who says 'I saw' over someone who says 'I heard.' Truth in turn rests on strength, which is life-breath. The Gayatri is named for protecting the life-breaths, and a teacher who teaches it protects the life of his student.