On one of his ministry websites, John MacArthur tells you that he is - calls himself - "the World's Premier Expository Preacher" - https://macarthurcenter.org/the-expositor/ .
And yes, he does call himself that. It's his centre, in his name, and every statement it publishes, especially if it's prominent, is thus endorsed as his statement until he retracts it as erroneous. And that page has said so since at least June 2021, and so for at least 3 and a half years:
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Why am I drawing your attention to this? Are we not meant to hide things in our brethren that are embarrassing or dishonourable? On the contrary, those who publicly represent Christ must expect scrutiny, and invite it; Paul said in 1 Corinthians 11:1, "Imitate me, just as I also imitate Christ", and in Philippians 3:17, "Brethren, join in following my example, and note those who so walk, as you have us for a pattern."
John MacArthur wants your attention to be drawn to this fact, so that you can sign up to learn from him. That's why he's put it in big type, at the top a main page of an eponymous ministry websites.
What to make of this?
For one thing, Jesus Christ forbids his servants to receive titles from men; how much more does he forbid men to award them to themselves?
Matthew 23:8 But you, do not be called ‘Rabbi’; for One is your Teacher, the Christ, and you are all brethren. 9 Do not call anyone on earth your father; for One is your Father, He who is in heaven. 10 And do not be called teachers; for One is your Teacher, the Christ.
Plainly this prohibition cannot be made absolute; it does not extend to titles that recognise and are used legitimately in connection with an office; Christ's apostles, inspired by his Spirit, used the title "apostle of Jesus Christ" to introduced themselves. Paul (1 Corinthians 15:10) told the Corinthians, again under inspiration, that he had worked harder than all the other apostles. But then, there, there were only a small handful of other apostles. Evidently, Paul said it knowing it to be objectively true - but let's also note the full context of what he had to say:
1 Corinthians 15:9 For I am the least of the apostles, who am not worthy to be called an apostle, because I persecuted the church of God. 10 But by the grace of God I am what I am, and His grace toward me was not in vain; but I laboured more abundantly than they all, yet not I, but the grace of God which was with me.
As far as I know, though, there is no office of "world's premier Bible expositor" that Jesus Christ appointed for someone to take up. Out of interest, when did MacArthur inherit this position, and who was his immediate predecessor?
Again, Paul said: "Imitate me, just as I also imitate Christ", 1 Corinthians 11, thereby drawing attention to his own example, which therefore cannot be absolutely wrong to do. But can you imagine Paul adding "and I am the world's premier imitator of Jesus Christ", even though that might actually have been true, given what we know of Paul's deep sufferings and what God, by the Holy Spirit, had to say about those sufferings?
You can make of John MacArthur awarding himself the title "the World's Premier Expository Preacher" what you will. I was quite sure that it wasn't me, so I'm certainly not disputing it on those grounds! Quite how MacArthur determined that he was the world's foremost explainer of the Bible, we are not told. We know that he is strongly against the concept of private revelations. We suppose he determined it some other way. However he determined it, he did think it was important to let us know.
Since you now know that John MacArthur has concluded that he is the world's premier expounder of God's word to man, and that he needed to tell you this, are you now helped to take him as seriously as such an important person should be taken?