The Six Books of Proclus on the Theology of Plato, Volume 2

For if the good is preservative of all beings, (on which account also it is desirable to all things) but that which is preservative and connective of the essence of every thing, is the one; for all things are preserved by the one, and dispersion removes every thing from essence;—if this be the case, the good will cause those things to which it is present, to be one, and will connect and contain them according to union. And if the one is collective and connective of beings, it will perfect every thing by its presence. Hence, therefore, it is good to all things to be united. If, however, union is of itself good, and good has the power of uniting, the simply good, and the simply one are the same, uniting and at the same time benefiting beings. Hence it is that those things which after a manner fall off from the good, are at the same time also deprived of the participation of the one. And those things which become destitute of the one, being filled with separation, are after the same manner likewise deprived of the good. Hence, goodness is union, and union is goodness, and the one is that which is primarily good.