the first and the last

31 But many that are first shall be last; and the last first.

Who do the first and last represent?

Those first financially (rich) and those last finacially (poor)?
Those first spiritually (church celebrities) and those last spiritually (church lay people)?
Those first in authority (leaders) and those last in authority (slaves)?

Anyone else?

re: the first and the last:
Repeatedly the Saviour says, "Many that are first shall be last; and the last shall be first." Jesus would have those who are engaged in His service, not eager for rewards, nor feel that they must receive compensation for all that they do. The Lord would have our minds run in a different channel; for He sees not as man sees. He does not judge by appearances, but estimates a man by the sincerity of his heart. {CS 339.1}
Those who have brought into their service the spirit of true sacrifice, of self-abasement, are the ones who will stand first at last. The laborers who were first hired, represented those who have an envious, self- righteous spirit, and claim that, for their services, preference should be given to them rather than to others. The householder said to the one who questioned his right to give more to others than to him, "Friend, I do thee no wrong: didst not thou agree with me for a penny?" I have kept my part of the agreement. {CS 339.2}
In a subordinate sense we should all have respect unto the recompense of the reward. But while we appreciate the promise of blessing, we should have perfect confidence in Jesus Christ, believing that He will do right, and give us reward according as our works have been. The gift of God is eternal life, but Jesus would have us not so anxious concerning rewards, as that we may do the will of God because it is right to do it, irrespective of all gain. {CS 339.3}

As the statement above mentioned:
Those first call to the service of the Lord (pioneers) and those last called(eleventh hour workers)