Albert Barnes on Luke 10:29

To justify himself. Desirous to appear blameless, or to vindicate himself, and show that he had kept the law. Jesus wished to lead him to a proper view of his own sinfulness, and his real departure from the law. The man was desirous of showing that he had kept the law; or perhaps he was desirous of justifying himself for asking the question; of showing that it could not be so easily settled; that a mere reference to the words of the law did not determine it. It was still a question what was meant by neighbour. The Pharisees held that the Jews only were to be regarded as such, and that the obligation did not extend at all to the Gentiles. The lawyer was probably ready to affirm that he had discharged faithfully his duty to his countrymen, and had thus kept the law, and could justify himself. Every sinner is desirous of justifying himself. He seeks to do it by his own works. For this purpose he perverts the meaning of the law, destroys its spirituality, and brings down the law to his standard, rather than attempt to frame his life by its requirements.

(f) "justify" Job 32:2, Lk 16:15, Rom 4:2, Gal 3:11, Jas 2:24 (g) "neighbour" Mt 5:43,44