On the Christian Faith (De fide)

The Arian argument from S. Mark 10:18 , “There is none good but one, that is, God,” refuted by explanation of these words of Christ.

15. The objection I have now to face, your sacred Majesty, fills me with bewilderment, my soul and body faint at the thought that there should be men, or rather not men, but beings with the outward appearance of men, but inwardly full of brutish folly— who can, after receiving at the hands of the Lord benefits so many and so great, say that the Author of all good things is Himself not good.

16. It is written, say they, that “There is none good but God alone.” I acknowledge the Scripture— but there is no falsehood in the letter; would that there were none in the Arians' exposition thereof. The written signs are guiltless, it is the meaning in which they are taken that is to blame. I acknowledge the words as the words of our Lord and Saviour— but let us bethink ourselves when, to whom, and with what comprehension He speaks.

17. The Son of God is certainly speaking as man, and speaking to a scribe,— to him, that is, who called the Son of God “Good Master,” but would not acknowledge Him as God. What he believes not, Christ further gives him to understand, to the end that he may believe in God's Son not as a good master, but as the good God, for if, wheresoever the “One God” is named, the Son of God is never sundered from the fullness of that unity, how, when God alone is said to be good, can the Only-begotten be excluded from the fullness of Divine Goodness? The Arians must therefore either deny that the Son of God is God, or confess that God is good.

18. With divinely inspired comprehension, then, our Lord said, not “There is none good but the Father alone,” but “There is none good but God alone,” and “Father” is the proper name of Him Who begets. But the unity of God by no means excludes the Godhead of the Three Persons, and therefore it is His Nature that is extolled. Goodness, therefore, is of the nature of God, and in the nature of God, again, exists the Son of God— wherefore that which the predicate expresses belongs not to one single Person, but to the [complete] unity [of the Godhead].

19. The Lord, then, does not deny His goodness— He rebukes this sort of disciple. For when the scribe said, “Good Master,” the Lord answered, “Why do you call Me good?”— which is to say, “It is not enough to call Him good, Whom you believe not to be God.” Not such do I seek to be My disciples— men who rather consider My manhood and reckon Me a good master, than look to My Godhead and believe Me to be the good God.