SB 2.10.25

gatiṁ jigīṣataḥ pādau
 ruruhāte ’bhikāmikām
padbhyāṁ yajñaḥ svayaṁ havyaṁ
 karmabhiḥ kriyate nṛbhiḥ
Word for word: 
gatim — movement; jigīṣataḥ — so desiring; pādau — the legs; ruruhāte — being manifested; abhikāmikām — purposeful; padbhyām — from the legs; yajñaḥ — Lord Viṣṇu; svayam — personally Himself; havyam — the duties; karmabhiḥ — by one’s occupational duty; kriyate — caused to be done; nṛbhiḥ — by different human beings.
Translation: 
Thereupon, because of His desiring to control movement, His legs became manifested, and from the legs the controlling deity named Viṣṇu was generated. By His personal supervision of this act, all varieties of human being are busily engaged in dutiful occupational sacrifice.
Purport: 

Every human being is engaged in his particular occupational duty, and such activities are visible as men go hither and thither. This is very prominently visible in big cities of the world: people are going all over the cities with great concern, from one place to another. This movement is not limited only to the cities, but is also visible outside the cities from one place to another, or from one city to another, by different means of vehicles. Men are moving by cars and rails on the roads, by subways within the earth and by planes in the sky for the purpose of business success. But in all these movements the real purpose is to earn wealth for comfortable life. For this comfortable life the scientist is engaged, the artist is engaged, the engineer is engaged, the technician is engaged, all in different branches of human activity. But they do not know how to make the activities purposeful to fulfill the mission of human life. Because they do not know this secret, all their activities are targeted towards the goal of sense gratification without control, and therefore by all this business they are unknowingly entering into the deep regions of darkness.

Because they have been captivated by the external energy of the Supreme Lord, they have completely forgotten the Supreme Lord Viṣṇu, and thus they have taken it for granted that this life, as presently manifested under the conditions of material nature, is all in all for enjoying the highest amount of sense gratification. But such a wrong conception of life cannot give anyone the desired peace of mind, and thus in spite of all advancement in knowledge by use of the resources of nature, no one is happy in this material civilization. The secret is that at every step they should try to execute sacrifices toward the path of world peace. The Bhagavad-gītā (18.45-46) also advises the same secret in the following verses.

sve sve karmaṇy abhirataḥ
 saṁsiddhiṁ labhate naraḥ
sva-karma-nirataḥ siddhiṁ
 yathā vindati tac chṛṇu

yataḥ pravṛttir bhūtānāṁ
 yena sarvam idaṁ tatam
sva-karmaṇā tam abhyarcya
 siddhiṁ vindati mānavaḥ

The Lord said to Arjuna: “Just hear from Me how one can attain the highest perfection in life simply by discharging his specified occupational duty. Man can attain the highest perfection of life by worshiping the Supreme Lord and by performing sacrifice for the sake of the Supreme Lord Viṣṇu, who is all-pervading and by whose control every living being acquires his desired facilities, according to his personal propensity.”

There is no harm in having different propensities in life because every human being is proportionately independent to chalk out the plan of his life by different occupations, but one should make it a point in his life to know perfectly well that he is not independent absolutely. One is certainly under the control of the Supreme Lord and under different agencies. Knowing this, one should make it a point that by his work and the result of his labor he serves the Supreme Lord as prescribed by the authorities expert in the transcendental loving service of the Supreme Lord Viṣṇu. For performing such occupational duties of life the leg is the most important instrument of the body because without the help of the legs one cannot move from one place to another, and therefore the Lord has special control over the legs of all human beings, which are meant for performing yajñas.