1)
What are the connotations of "va'Hashem He'emircha ha'Yom"?
2.
Ramban: Today is like Har Sinai, when Hashem elevated you and aggrandized you with your acceptance of the Torah, to be for Him a treasured nation over and above all the other nations. 1
1
Because to you alone did He give the Torah, not to any other nation, as the Pasuk states in Tehilim, 147:19 - 20.
2)
Where did Hashem say that they would be a treasured nation?
1.
Rashi: At Har Sinai, when He declared (Sh'mos, 19:5) "Vih'yisem Li Segulah!"