This is just one of those abstract logical statements. Nothing mystical. "Good" as an abstract quality, is that to which one is attracted; that which one wants. Even if you want to deny all things for yourself, or if you are attracted to "bad" things, still, that is what seems good to you.
You can travel toward good, or you can be pushed away from it. But your impetus is always in the direction of good. That is an absolute statement, only in that language has a common meaning to people. To say that good is what people are attracted to is to say Good is good, or, "When people make this sound, they are referring to something they like."
I'll leave the abstract meaning of "unidirectional" to your general experience. Good is unidirectional. All that means is that the abstract quality "good" has the abstract quality "unidirectionality." To over 90% of humanity, as I have experienced them, this would be the most boring discussion in the world. If it is interesting to you, I want to get to know you. In fact, I am specially burying this invitation, instead of setting it off in a paragraph, so that only non-bored readers will see it :-).
"Good" as an abstract quality, is a quality that resides in the eye of the beholder, like beauty. I could probably make a good logical argument for that, but I think it is self-evident. I know that legions of theologians and philosophers have debated it for centuries. But without an ax to grind around whose God is the greatest, there doesn't seem much of an argument that abstract qualities exist in some meaningful sense, outside of time, space, and matter. They are part and parcel of the thing they are attributed to; else they are part and parcel of the functioning mind that is attributing them (some are one way, and some are the other.) We think we attribute "goodness" to something we appreciate, when attributing goodness is really just the expression of being oriented positively toward something.
If someone who is a good logician wants to help me clarify my thinking, please, have at it.