"Behold, he is going out to meet you and when he sees you he will rejoice in his heart" ( Shemos 4:14). Hashem had sent Moshe to redeem Am Yisrael (3:10), but Moshe asked Hashem to send Aharon, Moshe's older brother, who had served as a prophet (Rashi 4:10). Moshe feared that were he to assume superiority over Aharon that it would cause resentment (Rashi 10:14). Instead, Hashem promised Moshe that Aharon would rejoice, not resent. Aharon's heart, which had the capacity to resist sibling rivalry and jealousy, would be rewarded with the choshen (breastplate worn by the Kohen Gadol- High Priest) (Rashi 10:14).
Years later, after Korach sought Aharon's kehuna (priesthood) and was killed, Hashem told Aharon, "Behold I have given you the gift of kehuna," (Bamidbar 18:8). "Behold" (Hineh) is an expression of joy, as in "Behold...he will rejoice in his heart" (Rashi).
Korach sinned because he was jealous and coveted a leadership position (Rashi 16:1). Aharon, who lost his leadership position, was not jealous, but rather happy with his lot (Avos 4:1).
This is the meaning of the expression "Behold". One must recognize that his lot is ordained by Hashem, and be happy with it. Everyone will be called by name, set in place and given a position. No one shall encroach upon your wealth or kingdom, even for as much as a hairsbreadth (Yoma 38b-39a).
The proof text for happiness with one's lot is, "when you eat of the labor of your hands, you are praiseworthy and all is well with you, " (Tehillim 128:2). This applies to family, wife and children, as well (128:3). The theme concludes with, "behold, for so is blessed the man who fears Hashem," (128:4). Fear of Hashem leads to the recognition of "Behold" and the happiness with one's lot that results.
Moshe refused to accept his mission of leadership for seven days, until Hashem became angry (Rashi 4:10). Moshe was punished in kind when his tenure as Kohein Gadol was terminated after seven days (Medrash Rabba Vayikra 11:6). At that point, Moshe sprinkled the oil of anointment on Aharon (Vayikra 8:30). The medrash (3:6) interprets the pasuk (Tehillim 133:2), "like the precious oil upon the head, running down the beard, the beard of Aharon," referring to this event. The medrash comments on the repetition of the word "beard", explaining that when Moshe saw the oil on Aharon's beard, he rejoiced as if it was running down his own. Moshe reciprocated Aharon's expression of joy and lack of jealousy.
This story is introduced by the pasuk, "Behold, how good and pleasant is the dwelling of brothers in unity." The same expression, "behold", describes the joy of these two great brothers, Moshe and Aharon. It also challenges all of us to eliminate jealousy and to happily accept the lot that Hashem has ordained for each and every one of us. Only then will we all be able to dwell as brothers in unity. How good and pleasant will it be!