The Tur and Kitzur Shulchan Aruch start the first siman with the Mishnah in Pirkei Avos (5:20).
Yehuda ben Teima says,be bold like a leopard – sometimes a person wants to do a mitzvah
and is ashamed to do so, because of people laughing at him.
Be bold like an eagle, referring to the eyes, that one should close their eyes from seeing bad,
because the starting point of doing עברות is the eyes. As the eyes see, the heart desires and
the body does the action.
Be swift like a deer, referring to the feet, be swift to go to do mitzvahs.
Be strong as a lion, referring to the heart, because strength in ‘עבודת ה is in the heart. The heart is the place of decision, make your decision for ‘עבודת ה strong. The Shulchan Aruch states that one should arise in the morning like a lion to serve his Creator, this means that if one will be מתגבר כארי, then he will be able to wake up in the morning and begin his day with  ‘עבודת ה and no excuse in the world will hold him back from ‘עבודת ה. The Yetzer Hora comes to the person in the winter and says to him, how can you get out of bed now, it’s cold outside,in the summer he says, the night is short, and you did not sleep enough. The Yetzer Hora has many other reasons besides this. However with one having his priorities in front of him clearly, nothing can stop him.