The Maharal of Prague explains that the number seven is always an indicator of shlemut. He brings this up most poignantly in his discussion of kriat shema and birchot kriat shema (Netivot Olam, N'tiv HaAvodah, ch. 7), explaining there that the oneness of HaShem as proclaimed at night is the same oneness of HaShem proclaimed during the day, so much so that night and day must be considered two halves of one whole, each part needing the other for its existence, as the pasuk reads, "vayahi erev, vayahi boker, yom echad" - there was an evening and there was a morning, one day" (Bereshit, ch. 1). The Maharal teaches that this point was emphasized by Chazal by splitting the total of seven b'rachot of kriat shema, four at night and three in the day, to indicate that the shlemut of seven only comes by understanding G-d's oneness at night and Gd's oneness during the day as the same oneness.
One might wonder, however, what would bring a person to believe that day and night were separate, and that the oneness of G-d would be fundamentally changed between these two times. At night, the Maharal explains, everything is in its hidden state, and, therefore, when one proclaims the unity of HaShem at this time, in the midst of the darkness, he proclaims that even the unknown, that which cannot be seen, is fundamentally bound with the unity of the Creator. In many ways this is the experience of G-d's Oneness in the simplest sense. The place that a person must bring himself to find G-d and His unity in the midst of the darkness transcends all the things of this world and returns him to a more essential reality in which G-d's unity is apparent, even though he cannot see it in this world at this time. When morning comes, and the things of this world become visible again, when their relationship to light, and thereby the light of G-d, is re-established, is it possible for a person to remember that simple unity that he experienced at night, when all these things and there connection to the light of G-d was completely hidden? According to the Maharal, a person must retain his knowledge of the simple unity of G-d as he is confronted by the multiplicity of this world in order to arrive at the shlemut of G-d, of himself, and of the world.
The Baal HaTanya expresses this idea a little differently. He wonders (Likutei Torah on Shir HaShirim) why the bitul, the nulification of self into the Oneness of G-d, which comes about through concentrated proclamation of the first pusuk of kriat shema, should then be followed by a command to love G-d. What point is there to speak of love once complete identification and unity with G-d has been attained? The Baal HaTanya answers, and the Mittler Rebbe explains further (Kuntrus Hitpa'alut), that this experience of unity is just the beginning of a love relationship with HaKadosh Baruch Hu, not the end. Such an experience is indeed, according to this approach, a prerequisite for any real love to be shared between man and G-d. The particularities of love that are to follow, the experience of G-d in the daytime - as the Maharal explained, is not a falling away from the experience of unity, G-d forbid, but rather a deepening and expansion of this experience.
This newfound experience of true love with HaKadosh Baruch Hu, a love rooted in and constantly mindful of G-d's unity and yet able to hold the beauty of multiplicity and expression, is held by the number seven and the aspect of Shabbat. Just as Shabbat is both a light onto itself and expression of the light of the entire week, so too all sevens. Seven, the aspect of malchut, of kingship, is able to be called both by its own name and by the name of the whole of which it seems only a part. This ability to hold both prat - the aspect of individuality and specificity - and clal - the aspect of unity and Oneness, is the special shlemut of the number seven. In these weeks between Pesach and Shavuot, we count seven, seven times. Also in the cycles of shmita and yovel - the sabbatical and jubilee years, we count seven, seven times. In this counting of seven times within seven, we place our shlemut in the context of HaShem's shlemut, building towards an even greater unity and contact with G-d as expressed, by 50 - the year of the yovel, the day of Shavuot (the day we receive the Torah), and the last gate of Binah - Understanding (the level of intimacy with G-d that Moshe Rabbeinu only achieved on the day of his death).
This mirroring and connection between the shlemut that we attain through seven and the shlemut of G-d in seven is indicated in the command to keep the weekly Shabbat in connection with and because HaShem made Shabbat after the six days of creation. As the pasuk reads, "and the seventh day is Shabbat to G-d, you shall not work...for in six days G-d made the heavens and the earth...and he rested on the seventh day." (Shemot, ch.20). May we be blessed to find shlemut in all our sevens, and to even find the seven within seven, which is seven, seven times - the ultimate awakening of G-d and man. May we be so blessed.