A.T. Robertson Commentary Matthew 19:17

"And he said unto him, Why askest thou me concerning that which is good? One there is who is good: but if thou wouldest enter into life, keep the commandments." — Matthew 19:17 (ASV)

Concerning that which is good (περ του αγαθου). He had asked Jesus in verse 16 "what good thing" he should do. He evidently had a light idea of the meaning of αγαθος. "This was only a teacher's way of leading on a pupil" (Bruce). So Jesus explains that "One there is who is good," one alone who is really good in the absolute sense.