Bhagavad Gita 8.15मामुपेत्य पुनर्जन्म दुःखालयमशाश्वतम्।नाप्नुवन्ति महात्मानः संसिद्धिं परमां गताः ॥

Birth is the home of pain or seat of sorrow arising from the body. Study the Garbhopanishad. There the nature of pain, i.e., how the child is confined in the womb, and how it is pressed during its passage along the vaginal canal and the neck of the womb or uterus, is described. Further it is much affected by the PrasutiVayu (the vital air which is responsible for the delivery of the child).Mahatmas (great souls) are free from Rajas and Tamas.Having attained Me This denotes KramaMukti or gradual liberation. The devotees who pass along the Devayana through the force of their Upasana, attain to Brahmaloka (the world of Brahma the Creator) or Satyaloka (the world of truth, the highest of the seven worlds) and there enjoy all the divine wealth and glory of the Lord and then attain to Kaivalya Moksha (final liberation) through the knowledge of Brahman, along with Brahma during the cosmic dissolution.Mahatmas or great souls who have attained Moksha do not come again to birth. Those who have not attained Me, take birth again in this world.