John Gill Commentary Luke 10:28

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

And he said unto him, you have answered right
It is so written, and read; and this, as if he should say, is the sum and substance of the law, and what that requires men should do; therefore,

do this, and you shall live ;
for the bare reading of it was not sufficient; though these men placed great confidence in reading this passage, or in reciting their phylacteries, of which this was a part, morning and night. Our Lord intimates by this, that, according to the tenor of the law, eternal life was not to be had without a complete and perfect performance of the duties of love to God, and to the neighbour, contained in these words; and this he suggests, in order to convict him of the impossibility of obtaining life by the works of the law, since such a performance cannot be made by man.