Nicodemus was a man described in John chapter three as a ruler of the Jews. Jesus called him a master of Israel, meaning that he was a teacher of the people. Nicodemus was engaged in conversation with the Lord concerning the new birth of water and the spirit. Jesus was explaining this birth not to be a fleshly birth, but one of the water of baptism and of the Holy Spirit.
When Nicodemus questioned this doctrine, the Lord asked him how he could be a master of Israel and not know these things. Though the doctrine may have been new to Nicodemus, Jesus seemed to feel that he should have understood it better at the time than he did. From the Lord’s point of view, there is certainly something to be expected of those who would be teachers, for they must certainly know the subject well enough to teach it.
While knowledge and understanding are certainly required of the teacher, would it surprise you to know that we all are called upon, at least to some extents, to be teachers? We, then, are all obligated to understand certain things well enough to communicate that knowledge to others. For example, at First Peter chapter three, we’re told at verse fifteen that we all are to be prepared to answer any man concerning the hope that is in us. It seems that everyone must feel that there is some reason to be what ever they are religiously speaking, even if that affiliation came to be for no reason stronger than family influence or friends who swayed us that way.
Beyond this, some have no greater reason at all for their "spiritual persuasion". Greater conviction is certainly to be expected of members of the Lord’s church, and Peter calls upon every New Testament Christian to have not only such a conviction, but to be also able to defend it. Sadly, many are unable to do so, and appear unaware that there is in fact a vast difference in truth and error, or seem to feel that most anything done in the name of religion is alright. In reality, Jesus declared that such could not be further from the truth.
At Matthew chapter fifteen, Jesus referred at verses eight and nine to a prophecy about those who would seem to draw nigh to the Lord with their speech and honor Him with the things they would say. However, the Lord said the worship of such individuals was vain who taught for doctrines the commandments of men.
Quite obviously, from the lips of Jesus Himself, everything taught in the name of religion is not alright, not even among many who name the name of Christ, for it is impossible to honor Him without honoring His Word in every wit. Can a man be a "master of Israel", and not know these things? Every Christian is called upon to be a teacher, and every teacher is called upon to both live and defend the truth, knowing the difference in doctrinal right and wrong, truth and error.