Why do we say "You" when we talk to Hashem in the second person singular, but when we refer to rebbe we refer to him in the third person ("the rabbi")?
We often use both towards God, even in the same blessing (!), e.g.: "Blessed are You (second person)… [Who] gave the Torah ["Noten HaTorah"=He (third person) gave, not You gave, not "Natata HaTorah"], because it's important to remember that He is our Father and also our King. We must remember also to love Him, as well as be in awe of Him. On the other hand, regarding people, we clearly see they are just flesh and blood, and may have a tendency not to respect them, so it's often customary, though not obligatory, to speak in the third person.