A.T. Robertson Commentary Luke 10:28

"And he said unto him, Thou hast answered right: this do, and thou shalt live." — Luke 10:28 (ASV)

Thou hast answered right (ορθως απεκριθης). First aorist passive indicative second singular with the adverb ορθως. The answer was correct so far as the words went. In Mr 12:34 Jesus commends the scribe for agreeing to his interpretation of the first and the second commandments. That scribe was "not far from the kingdom of God," but this lawyer was "tempting" Jesus.

Do this and thou shalt live (τουτο ποιε κα ζηση). Present imperative (keep on doing this forever) and the future indicative middle as a natural result. There was only one trouble with the lawyer's answer. No one ever did or ever can "do" what the law lays down towards God and man always. To slip once is to fail. So Jesus put the problem squarely up to the lawyer who wanted to know

by doing what . Of course, if he kept the law

perfectly always , he would inherit eternal life.