What is the gist of the covenant that Lavan made with Yakov? Why did he begin with the word "v'Atah"?
Seforno: What he is saying is 'Now that it is clear that I am not out to harm you, 1 let us make a covenant that will also guarantee that you will not harm me!'
Oznayim la'Torah: Based on the principle that "ve'Aah" implies Teshuvah, Lavan was saying that, granted, he had chased after Yakov to do him harm, but now that he had decided to follow the instructions of Hashem his G-d, let bygones be bygones and let us make a covenant of peace.
To whom (what) was he referring when he said 'v'Hayah l'Eid Beini u'Veinecha'?
Rashi: He was referring to Hakadosh-Baruch-Hu. 1
Ramban 2 : He was referring to the covenant, 3 including oaths and curses that would take effect on whoever would break it. Alternatively, he was referring to something concrete on which the covenant would take effect. 4
רש"י: והיה לעד - הקדוש ברוך הוא: אולי הברית תהיה לעד?
גור אריה: 'ברית' זה לשון נקבה, ואם הברית מעידה, צריך היה לכתוב 'והייתה לעד'.