Genesis 29:2

And he looked and saw, and behold (there was) a well in a field, and behold there three flocks of sheep lying near it; because from that well they watered the flocks; and a great stone was laid upon the mouth of the well.

AND HE LOOKED, AND BEHOLD A WELL IN THE FIELD, AND LO THREE FLOCKS OF SHEEP LYING THERE BY IT. Scripture tells this story at length in order to let us know that they that wait for the Eternal shall renew their strength, and the fear of Him gives strength. For here our father Jacob is coming from the journey and he is tired, yet he alone rolls away the stone, a task which required all the shepherds. The many shepherds and all the watchmen of the three flocks of sheep could not shift the rock.
With respect to this chapter, our Rabbis in Bereshith Rabbah also have a secret which alludes to the future. For it happened to him that he came to Haran by way of the well, and only three of all the flocks were gathered. He arrived at the time when the stone was yet upon the mouth of the well, and the flocks waited for the water thereof. Likewise, the matter which is narrated here is all for the purpose of letting it be known that Jacob will succeed in this venture and will have children worthy of the fulfillment of this allusion. For the well alludes to the Sanctuary, and the three flocks of sheep are symbolic of the pilgrims ascending to the Sanctuary during the three festivals., and Succoth. See Deuteronomy 16:16. The expression, For out of that well they watered the flocks, alludes to the fact that they drew holy inspiration from the pilgrimages to the Sanctuary. It may be that it alludes to the verse, For out of Zion shall go forth Torah — which has been likened to water,, 55:1, Baba Kamma 17a. and the word of the Eternal from Jerusalem. — And thither were all the flocks gathered — from the entrance of Hamath unto the Brook of Egypt.. — And they rolled the stone from the well’s mouth and watered, for they drew holy inspiration therefrom. And they put the stone back to lie dormant until the next festival.

רבצים עליה, waiting until all the shepherds would gather there with their flocks and they would roll the rock off the top of the well.

והאבן גדולה על פי הבאר, this was a precautionary measure to ensure people would not fall into the well and drown, or that they would not draw water from the well if not entitled to this.

וירא והנה באר.. רבצים עליה, the word עליה means “near it,” just as in Numbers 2,20 when the positions of the various army groups of the Israelites are described and the Torah writes ועליו מטה מנשה. The meaning clearly cannot be that the tribe of Menashe was positioned on top of the tribe of the tribe of Ephrayim, but that the tribe of Menashe was positioned close to the tribe of Ephrayim. The term על in the sense of “near, close by,” occurs numerous times in Scripture.

והאבן גדולה, seeing that there was no other source of water nearby to water the flocks of the people of Charan, the local people had placed an extremely large and heavy rock on top of it so that only in the presence of all the shepherds would the flocks be watered so as to ensure a fair distribution of the available water. This would also help to avoid wasting water remaining in the troughs when no other flock had already lined up at the troughs. Placing such a large stone on the well then was a device designed to help everyone entitled to this water to receive his fair share in the presence of all the shepherds.