As Iron Sharpens Iron - an iron(steel) will bring a Sword(the Word[or your words{that is your thinking and ability to Reason} to a better edge when it is properly whetted against it. So one person or 'friend', can, through discussion with you, cause you, to reflect and meditate upon an issue from another Point-of-view. This meditation can have it's effect on you and may lead you, like a Horse To Water, to See Things in a different Light. So Whetting Your Appetite(for some thing) Much like a salesman whets the appetite of the Mark, or a Brother whets the appetite of a Neophyte for the Word. And so through Brotherly Love(castigation[or castration of neophyte on his journey to (eunuch) priesthood]) your Sword(oration) can too become Sharpened(cleverer) too as you Seek the Light brother.