I sent you - In the commission given you to preach the gospel. You have not labored or toiled in preparing the way for the great harvest which is now to be gathered in.
Other men laboured -
(1) The prophets, who long labored to prepare the way for the coming of the Messiah.
(2) the teachers among the Jews, who have read and explained the law and taught the people.
(3) John the Baptist, who came to prepare the way. And,
(4) The Saviour himself, who by his personal ministry taught the people, and prepared them for the success which was to attend the preaching of the apostles.
Especially did Jesus lay the foundation for the rapid and extensive spread of the gospel. "He" saw comparatively little fruit of his ministry. He confined his labors to Judea, and even there he was occupied in sowing seed which chiefly sprang up after his death. From this we may learn:
1. That the man who is crowned with eminent success has no cause of "boasting" over others, any more than the man who reaps a field of grain should boast over the man who sowed it. The labor of both is equally necessary, and the labor of both would be useless if God did not give the increase. Compare 1-Corinthians 3:6.
2. We should not be discouraged if we do not meet with immediate success. The man that sows is not disheartened because he does not see the harvest "immediately" spring up. We are to sow our seed in the morning, and in the evening we are not to withhold our hand, for we know not whether shall prosper, this or that; and we are to go forth bearing precious seed, though "weeping," knowing that we shall come again rejoicing, bearing our sheaves with us, Ecclesiastes 11:4; Psalm 126:6.
3. Every part of the work of the ministry and of teaching men is needful, and we should rejoice that we are permitted to bear any part, however humble, in bringing sinners to the knowledge of our Lord and Saviour Jesus Christ, 1-Corinthians 12:21-24.

I sent you to reap,.... To preach the Gospel, and gather in souls by your ministry; referring to the mission of them in Matthew 10:6;
that whereon ye bestowed no labour; being sent to the Jews, who had the writings of the prophets, and were versed in them; and had learned from them that the Messiah was to come, and were now in general expectation of him; so that they had nothing more to do, than to declare to those persons who were cultivated by the prophets, and were like to ground tilled and manured, that the Messiah was come, and the kingdom of heaven was at hand.
Other men laboured; the prophets, and John the Baptist:
and ye are entered into their labours; to finish the work they had begun, and which was almost done to their hands.

I sent you, &c.--The I is emphatic--I, the Lord of the whole harvest: "sent you," points to their past appointment to the apostleship, though it has reference only to their future discharge of it, for they had nothing to do with the present ingathering of the Sycharites.
ye bestowed no labour--meaning that much of their future success would arise from the preparation already made for them. (See on John 4:42).
others laboured--Referring to the Old Testament laborers, the Baptist, and by implication Himself, though He studiously keeps this in the background, that the line of distinction between Himself and all His servants might not be lost sight of. "Christ represents Himself as the Husbandman [rather the Lord of the laborers], who has the direction both of the sowing and of the harvest, who commissions all the agents--those of the Old Testament as well as of the New--and therefore does not stand on a level with either the sowers or the reapers" [OLSHAUSEN].

I sent you to reap that whereon ye bestowed no labour. The verb "sent" is past, and refers to some event before the present incident. The disciples had baptized multitudes, "more disciples than John" (John 4:1); so many that John's disciples reported "all men come unto him" (John 3:26). They had baptized these (John 4:2), reaping the fruit of John's labors.

I - he Lord of the whole harvest, have sent you - He had employed them already in baptizing, John 4:2.