Ambrose of Milan

However, rightly so, a man has not many, but two feet; for four feet belong to wild animals and beasts, and two to birds. Therefore, a man is like a bird, who seeks lofty things with his sight and flies with a certain stroke of the senses' keenness. And therefore it is said about him: Your youth will be renewed like the eagle's; because he is closer to heavenly things and higher than eagles, who can say: But our conversation is in heaven.