Rom 2:20

“But you have the form of knowledge and truth not in deeds and not in merits, but "in the law," relying on it as on a depiction of virtue. So someone, having a royal portrait in his possession, copies nothing from it himself, while those who do not have it, and without even seeing it, faithfully imitate it. So then, every teacher writes and imprints in the souls of his students the knowledge of good, and therefore truth itself. If he carries this out in practice as well, he will be perfect; otherwise he will be like those now condemned by the apostle. Some understood "form" to mean a pattern of knowledge that is not genuine. You have, he says, knowledge and piety that is not true, but counterfeit and covered with a false appearance.”

“Second, he touches on those who are on the way to knowledge they have not yet attained, in one way through lack of full instruction; hence he says, an instructor of the foolish, i.e., of those who have not yet received wisdom who are said to be instructed, i.e., free from ignorance which is present in everyone from the beginning when they are first instructed: do you have children? Discipline them (Sir 7:23). In another way, through lack of age, as children. Hence he says, a teacher of infants: where is the teacher of little ones? (Isa 33:18). A third group are already advanced in knowledge, but they need instruction from the wise in order to possess the authoritative sayings of wisdom as their rule or pattern. In regard to this he says, having the form of knowledge: follow the pattern of the sound words which you have heard from me (2 Tim 1:13); mark those who so live as you have an example in us (Phil 3:17). However, people so patterned must be instructed by the authority of their forebears, if they are to know what has been handed down in the law. Therefore, he says, of knowledge: wisdom gave him knowledge of holy things (Wis 10:10). This is also necessary if they are to know the true understanding of what has been handed down. That is why he says, and of truth: send out your light and your truth (Ps 43:3).”

“These things are true, because this is the task of the law: to teach the ignorant, to subject the wicked to God, to provoke those who by the worship of idols are ungodly to trust in a better hope by the promise which is given through the law. The teacher of the law is right to glory in these things, because he is teaching the form of truth. But if the teacher does not accept the Expected One whom the law has promised, he glories in vain in the law, to which he is doing harm as long as he rejects the Christ who is promised in the law. In that case he is no more learned than the fools, nor is he a teacher of children, nor is he a light to those who are in the darkness, but rather he is leading all of these into perdition.”