And knowest his will, and approvest things excellent, etc. He now concedes to them the knowledge of the divine will, and the approval of things useful; and this they had attained from the doctrine of the law. But there is a twofold approval, -- one of choice, when we embrace the good we approve; the other of judgment, by which indeed we distinguish good from evil, but by no means strive or desire to follow it. Thus the Jews were so learned in the law that they could pass judgment on the conduct of others, but were not careful to regulate their life according to that judgment. But as Paul reproves their hypocrisy, we may, on the other hand, conclude, that excellent things are then only rightly approved (provided our judgment proceeds from sincerity) when God is attended to; for his will, as it is revealed in the law, is here appointed as the guide and teacher of what is to be justly approved. [1]

Footnotes

1 - There are two expositions of the words, dokimazeis ta diapheronta, which may be sustained according to what the words signify in other places. The first word means to prove, or test, or examine, and also to approve; and the second signifies things which differ, or things which are excellent. "Thou provest, or, distinguishest things which differ," is the rendering of Beza, Pareus, Doddridge, and Stuart: "Thou approvest things excellent or useful," is the rendering of Erasmus, Macknight, and others. The first is the most suitable to the context, as knowledge, and not approval, is evidently intended, as proved by the explanatory clause which follows, -- "being instructed out of the law." -- Ed.

And knowest his will - The will or commands of God. This knowledge they obtained from the Scriptures; and of course in this they were distinguished from other nations.
And approvest - The word used here is capable of two interpretations. It may mean either to distinguish, or to approve. The word is properly and usually applied to the process of testing or trying metals by fire. Hence, it comes to be used in a general sense to try or to distinguish anything; to ascertain its nature, quality, etc.; Luke 12:56. This is probably its meaning here, referring rather to the intellectual process of discriminating, than to the moral process of approving. It could not, perhaps, be said with propriety, at least the scope of the passage does not properly suppose this, that the Jew approved or loved the things of God: but the scope of the passage is, that the Jew valued himself on his knowledge of what was conformable to the will of God; see the notes at Romans. 14.
The things that are more excellent - The word translated here "more excellent" denotes properly the things that differ from others, and then also the things that excel. It has an ambiguity similar to the word translated "approved." If the interpretation of that word above given is correct, then this word here means those things that differ from others. The reference is to the rites and customs, to the distinctions of meats and days, etc., prescribed by the Law of Moses. The Jew would pride himself on the fact that he had been taught by the Law to make these distinctions, while all the pagan world had been left in ignorance of them. This was one of the advantages on which he valued himself and his religion.
Being instructed - That is, in regard to the one God, his will, and the distinguishing rites of his worship.

Knowest his will - Hast been favored with a revelation of his own will, immediately from himself.
The things that are more excellent - τα δισφεροντα, The things that differ - that revelation which God has given of himself makes the nicest distinctions between right and wrong; between vice and virtue; showing how you should walk so as to please God, and, consequently, acquire the most excellent portion that human spirits can have on this side heaven: for all these blessings ye acknowledge to receive from your law, being instructed, κατηχουμενος, being catechized, from your infancy, in the knowledge of Divine things.

And knowest [his] will, and (n) approvest the things that are more excellent, being instructed out of the law;
(n) Can test and discern what things swerve from God's will.

And knowest his will,.... Not the secret will or purpose of God; nor his revealed will in the Gospel, for of this they were ignorant; but his declared will in the law, showing what is to be done, and what is not to be done: to know which in express terms was a privilege, that other people had not; but then the bare knowledge of this will be of no avail: for persons may know their Lord's will, as the Jews did, and not do it, and so be worthy to be beaten with many stripes:
and approvest the things that are more excellent: or "triest the things that differ"; from one another, and from the will and law of God; or as the Syriac, "discernest" "things that are convenient"; agreeable, which are fit and ought to be done: and having tried and discerned them, they approved of them in their judgment as the things more excellent; but then they did not put these excellent things in practice which they approved of; and the knowledge and approbation they had of these things, arose from their
being instructed out of the law, and not the Gospel; for the excellent things of the Gospel, they had no discerning, knowledge and approbation of; see Philippians 1:10.

approvest the things that are excellent--"triest the things that differ" (Margin). Both senses are good, and indeed the former is but the result of the latter action. (See on Philippians 1:10).