Surah 19. Maryam, Ayah 43

I.e., a cognition of God's existence and uniqueness through intellectual insight (cf. {6:74-82}).

Some are more receptive of Light than others. It is their duty and privilege to guide and point to the right Way.

Sawiyan-right, smooth, even; complete, perfect; hence the derived meaning: in xix. 10, in full possession of all the physical senses; in that context, 'not dumb': in xix. 17, when the angel appears in the form of a man, 'completely like' a man, a man 'in all respects.'