One of the strongest themes in The Lion King is the importance of family, especially when it comes to Simba and Mufasa's father-son relationship. We are constantly reminded through Mufasa's wisdom that young Simba has some big paws to fill.
Which is why this crucial image is all the more excellent. After Mufasa rescues Simba from the hyenas, he tells his disobedient son that he'd like a word with him. Cowed, Simba approaches his father. As he walks forward, he steps in Mufasa's paw print and sees that it's basically 10 times the size of his.
This image serves to remind Simba—and the audience—that he has a very long way to go before he will have the wisdom and bravery necessary to become king.