Read the passage and answer the questions on the basis of your comprehension: (96 to 100)
The most important distinction between the animal man and others is, that the animal is very soon satisfied and retires within the limits of its necessities, the greater part of its earnings being necessary for its own preservation and the preservation of race. Like a retail shop keeper, it has no large profit from its commerce. But man, if the bulk of its earnings must be spent in paying the interest to its bank. Most of its earnings are employed in mere endeavor to live. But man, if its commerce, is a big merchant: he does a great deal more than he is absolutely compelled to spend. Therefore, there is a vast excess of earnings in man‘s life, which gives him the freedom to be useless and irresponsible to a great measure. There are large outlying tracts, surrounding his necessities, where he has objects that are ends to themselves. The animals must have knowledge, so that their knowledge can be employed for use, in the service of their life. But there they stop. They must know their surroundings in order to be able to procure shelter and seek their food, some properties of things in order to build their dwellings some signs of different seasons to be able to get ready to adapt themselves to the changes. Man, also must have these in order to live. But man has a surplus where he can proudly assert that knowledge is freed. With man, knowledge is freed. Here he has the pure employment of his knowledge because their knowledge is freed from the necessity of life. Thus, this fund of surplus his science and philosophy thrive.

What does the author mean by “Man also must know because he must live”?