Srimad Bhagavatam Canto 09, Chapter 18, Text 43

SB 9.18.43

sri-purur uvaca
ko nu loke manusyendra
 pitur atma-krtah puman
pratikartum ksamo yasya
 prasadad vindate param
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
Puru replied: O Your Majesty, who in this world can repay his debt to his father? By the mercy of one’s father, one gets the human form of life, which can enable one to become an associate of the Supreme Lord.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
The father gives the seed of the body, and this seed gradually grows and develops until one ultimately attains the developed human body, with consciousness higher than that of the animals. In the human body one can be elevated to the higher planets, and, furthermore, if one cultivates Krsna consciousness, one can return home, back to Godhead. This important human body is obtained by the grace of the father, and therefore everyone is indebted to his father. Of course, in other lives one also gets a father and mother; even cats and dogs have fathers and mothers. But in the human form of life the father and mother can award their son the greatest benediction by teaching him to become a devotee. When one becomes a devotee, he achieves the greatest benediction because he completely averts the repetition of birth and death. Therefore the father who trains his child in Krsna consciousness is the most benevolent father in this world. It is said:
janame janame sabe pita mata paya
 krsna guru nahi mile bhaja hari ei
Everyone gets a father and mother, but if one gets the benediction of Krsna and guru, he can conquer material nature and return home, back to Godhead.