The Alter Rebbe derives this from the following verses: “I was young and then I became old,” was said by an angel referred to as “the Minister in Charge of This World” (Yevamos 16b). Meaning, that only spiritual levels connected to this limited world (like that angel) can be called “young” or “old” since only something limited by time can become old. This is not the case, however, regarding Hashem, like it says (Zohar 199a): “before the Holy One Blessed Be He is there the idea of becoming old?”, since He is the one that “I Hashem never change”, and since He is totally unchanging and eternal, beyond time, there is no idea of being “old”.
Therefore, because Hashem is eternal, “the eyes of man will never be satisfied” (Mishlei 27:20) in looking to understand and connect to the Infinite Truth of Hashem. The meaning of ‘the eyes of man’ is an allusion to (Shir Hashirim 1:15): “your eyes are like the eyes of doves” that love to gaze at each other, so too a wise man will love to intellectually “gaze upon the Glory of the King”, by contemplating His greatness.
