On Shabbos mincha we say אתה אחד ושמך אחד ומי כעמך ישראל גוי אחד בארץ - You are One and Your Name is One and who is like Your nation Israel one people in the land.
Friday night corresponds to the first Shabbos of creation - שבת של מעשה בראשית. That is expressed in the liturgy of Friday night where we say ויכולו השמים והארץ etc. The story of creation. Shabbos morning corresponds to the Shabbos when the Torah was given [according to the gemara the Torah was given on Shabbos]. That is ALSO reflected in the liturgy ישמח משה וכו' ושני לוחות אבנים הוריד בידו - The giving of the asseres hadibros. Shabbos afternoon corresponds to the Shabbos of the end of days the yom shekoolo Shabbos. אתה אחד - the unity of Hashem.
But Hashem limits Himself [kiviyachol]. His Oneness and unity cannot be revealed on its own. He needs US. אתה אחד ושמך אחד - Indeed Hashem You are One, but that is only revealed fully when ומי כעמך ישראל גוי אחד בארץ - Who is like Your nation that is One people in the land. We are called a גוי which comes from the word גויה - organism. We are one integral organism. [The gentiles are not really goyim but the term is borrowed to describe gentile nations. So goyim aren't really goyim!] But only בארץ. The Maharal established a principal - the Jews are only a ציבור - a community, in the Land of Israel. This idea is expanded upon by the Avnei Nezer [O"C 314/4] the Rogochover [Shu"t Tzaphnas Paaneach 343] and the Lubavitcher Rebbe in his sichos [see also Chavatzeles Hasharon Bamidbar page 336 and what is written here]. When we are one nation, with complete achdus, but only in Israel. Chutz La-aretz separates us into individuals.
When is Hashem revealed in His unity and oneness? When we are one nation and DAVKA in the Land of Israel. When we and the gentiles realize this the geula will come. And when the geula comes both we and the gentiles will realize this...:-).
[Based on the Holy Books]
One note - why do we ask a rhetorical question - ומי כעמך ישראל - Who is like your nation Israel?! Why don't we say definitively אין כעמך ישראל - there is none like your nation Israel. See Pachad Yitzchak Shabbos Maamar 13. And bi-chlal - see Pachad Yitzchak. A delight to the heart, mind and soul.....:-) [For those who have trouble comprehending we have quite a few shiurim on Yutorah BS"D].
לזכות נעכא גיטל בת רחל אסתר לזרעא חייא וקיימא זרעא די לא יפסוק ולא יבטול מפתגמי אורייתא