What does the phrase mean "many are called but few are chosen"?

What is the meaning of “the last shall be first and the first last, for many are called but few chosen” (Matthew 20:16)?

The surface meaning of the first sentence, which occurs also in Matthew 19:30, is that the position will be reversed; the last taking the first place and the first taking the last place, but this is not at all what the parable teaches.

What is in view is rather the equality of last with first, and of first with last, and I submit that this is exactly what the words mean; the last shall be as the first, and the first as the last. Those called in the early days of our Lord’s ministry, and those called in the last days of the Christian era, will be on an equality.

The closing words are undoubtedly difficult, but I believe they mean, that, as far as character of service goes, though the number of those called is great, those chosen for special service, like the apostles, are few in number. Such will undoubtedly receive special awards in the Kingdom, e.g., as above, “sitting on twelve thrones judging the twelve tribes of Israel.” As far, however, as the common blessings of the redeemed are concerned— Eternal Life, Membership of Christ’s Body, Sonship, etc. there will be equality, though the differences implied by rewards will be eternal.