Sree Sree Guru Gaurangau Jayatah!
After eight million births we have got this precious human birth, the Supreme Lord is pleased by creating human beings because human beings have got the discriminating power between eternal and non-eternal, good deeds and bad deeds, they have got the capability to worship the Lord. But other living beings have got no such conscience, discriminating power. So it is said `Shubhasya shighram, ashubhasya kalaharanam’— when there will be good desire, we should do it immediately, otherwise later there might be some hindrance and obstacle to it and when there will be evil desire, you should make late to do it, you should not do it immediately— this is Ravana’s advice to Lakshman. There is no guarantee that next we shall get human birth. It is stated in the Gita (8.6) — yam yam vapi smaran bhavam tyajaty ante kalevaram / tam tam evaiti kaunteya sada tad-bhava-bhavitah— Whatever we shall think at the time of death, we shall get birth accordingly.
—Srila Bhakti Ballabh Tirtha Goswami Maharaj