Sāstra says, viṣayaḥ khalu sarvataḥ syāt (SB 11.9.29). These necessities of life, they can be obtained in any form of life. There is no scarcity. But the human form of life, if it is wasted only for these facilities of life—eating, sleeping, mating and defending—then what is the credit of getting a human form of life? The śāstra therefore says, tasyaiva hetoḥ prayateta kovidaḥ. In human form of life one should try to achieve that perfection which was not obtained in previous lives after wandering heaven and hell and all species of life. Bhramatām upary adhaḥ. Upari adhaḥ means upwards and downwards.
And we are wandering: sometimes downwards, sometimes outwards, sometimes poor, sometimes rich, sometimes man, sometimes dog, sometimes tree, sometimes demigod. In this way, we are wandering. Caitanya Mahāprabhu therefore says, ei rūpe brahmāṇḍa bhramite kona bhāgyavān jīva (CC Madhya 19.151). We are wandering in this way in different species of life, in different planets, but somehow or other, if one is fortunate, he comes in contact with a devotee by the grace of Kṛṣṇa. Guru-kṛṣṇa-kṛpāya pāya bhakti-latā-bīja.