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SB 11.9.29

labdhvā su-durlabham idaṁ bahu-sambhavānte
 mānuṣyam artha-dam anityam apīha dhīraḥ
tūrṇaṁ yateta na pated anu-mṛtyu yāvan
 niḥśreyasāya viṣayaḥ khalu sarvataḥ syāt
Synonyms: 
labdhvā — having obtained; su-durlabham — that which is very difficult to obtain; idam — this; bahu — many; sambhava — births; ante — after; mānuṣyam — human form of life; artha-dam — which awards great value; anityam — not eternal; api — although; iha — in this material world; dhīraḥ — one who has sober intelligence; tūrṇam — immediately; yateta — should endeavor; na — not; patet — has fallen; anu-mṛtyu — always subject to death; yāvat — as long as; niḥśreyasāya — for ultimate liberation; viṣayaḥ — sense gratification; khalu — always; sarvataḥ — in all conditions; syāt — is possible.
Translation: 
After many, many births and deaths one achieves the rare human form of life, which, although temporary, affords one the opportunity to attain the highest perfection. Thus a sober human being should quickly endeavor for the ultimate perfection of life as long as his body, which is always subject to death, has not fallen down and died. After all, sense gratification is available even in the most abominable species of life, whereas Kṛṣṇa consciousness is possible only for a human being.
Purport: 

Material life essentially means repeated birth and death. Even the lowest forms of life, such as reptiles, insects, pigs and dogs, have ample opportunity for sense gratification. Even ordinary houseflies have a busy sex life and thus multiply rapidly. Human life, however, enables one to understand the Absolute Truth and is therefore full of grave responsibility. Since the valuable human life is not eternal, we should do the needful to achieve the highest perfection, Kṛṣṇa consciousness. Before death appears, we should seriously cultivate our real self-interest.

One can experience Kṛṣṇa consciousness in the association of devotees of the Lord. Without their association, one is in danger of being attracted to an impersonal conception of life, which causes one to fall away from devotional service to the Absolute Truth. Or, being discouraged by one’s failure to understand the Absolute Truth, one may return to the false platform of sense gratification. In conclusion, human life is meant for cultivating Kṛṣṇa consciousness under the guidance of the experienced, self-realized devotees of the Lord.