What is the meaning of "Libavtini"?
Shabbos 53b: It denotes closeness.
Rashi: You drew My heart to you. Malbim (Melitzah) - this is clinging of Lev to Lev. Until now, our clinging was via understanding in the brain. From now it will be via arousal of the Nefesh in Avodah, in the heart, which is the source of the power of arousal and life forces.
What do we learn from "[Libavtini Achosi Chalah Libavtini] b'Achas me'Einayich"?
Torah Temimah citing Shabbos 88b: At first [when Yisrael accepted Torah], we drew close to Hashem with one eye. Later [through keeping Torah], we drew close with both 1 .
Rashi: There are many good features in you. Even if you had only one of them, I would endear you exceedingly, and all the more so since you have all of them!
Seforno: In the days of David, Hashem was pleased with the king, but not with Evyasar Kohen Gadol 2 .
Malbim (Melitzah): Until now, two eyes were needed to see - the eye of vision and understanding of Elokus in the great Merkavah (the general existence), and the eye of understanding of Elokus in the Nefesh, which is the small Merkavah, like I explained above (1:15). Now that you drew My heart to you with one of your eyes, understanding via investigation of the existence and its conduct is not needed, only looking at the Nefesh itself. It will descend to oversee its small world, to designate all its powers and offer it for a Korban in front of Melech ha'Kavod.
Malbim (Mashal): You look at me with only one of your eyes. The other looks at Chadrei Shlomo and Bnos Tziyon, who guard.
What is "b'Achad Anak mi'Tzaveronayich"?
Rashi #1: With one of the necklaces of your ornaments - these are ornaments of Mitzvah that Yisrael are distinguished via them.
Rashi #2: One of your Avos - "Echad Hayah [Avraham]" (Yechezkel 33:24) - Meyuchad (special). He was called "ha'Adam ha'Gadol ba'Anakim" (Yehoshua 14:15).
Seforno: In the days of David, Hashem was pleased with "Benyahu ben Yehoyada Al ha'Keresi v'Al ha'Plesi" (Shmuel II, 20:23), but not with Yo'av (the Sar Tzava).
Malbim (Melitzah): Now it suffices to have one appointment of the practical intellect, for Yir'ah and Avodah; there is no needed for investigative intellect.
Malbim (Mashal): Only one of them is special for me; the other is for Shlomo.