Matthew 20:16 So the last shall be first, and the first last: for many be called, but few chosen. - Free Bible Online

      16. So the last shall be first, and the first last--that is, "Take heed lest by indulging the spirit of these murmurers at the penny given to the last hired, ye miss your own penny, though first in the vineyard; while the consciousness of having come in so late may inspire these last with such a humble frame, and such admiration of the grace that has hired and rewarded them at all, as will put them into the foremost place in the end."
      for many be called, but few chosen--This is another of our Lord's terse and pregnant sayings, more than once uttered in different connections. (See Mt 19:30; 22:14). The "calling" of which the New Testament almost invariably speaks is what divines call effectual calling, carrying with it a supernatural operation on the will to secure its consent. But that cannot be the meaning of it here; the "called" being emphatically distinguished from the "chosen." It can only mean here the "invited." And so the sense is, Many receive the invitations of the Gospel whom God has never "chosen to salvation through sanctification of the Spirit and belief of the truth" (2Th 2:13). But what, it may be asked, has this to do with the subject of our parable? Probably this--to teach us that men who have wrought in Christ's service all their days may, by the spirit which they manifest at the last, make it too evident that, as between God and their own souls, they never were chosen workmen at all.

JFB.