When Alma took time to teach his sons on an individual basis, Corianton received much more attention than his older brothers. Instead of preaching the gospel, he had been chasing the harlot Isabel and justifying his actions by questioning the justice of God (Alma 39-42). Here, we learn that he had repented to become a useful servant of the Lord—much like his father had done years before him.
“Tucked in the ongoing story of the Nephite wars we find a reference to the change that Corianton made in his personal life. Peace was in the land again and the people prospered ’because of their heed and diligence which they gave unto the word of God, which was declared unto them by Helaman, and Shiblon, and Corianton, and Ammon and his brethren’ (Alma 49:30). Notice who was back on his mission again. Hurrah! Through a parent-child interview, Alma brought about a transformation in the life of his beloved son, and this united family of missionaries and Nephite ministers made an incredible difference in the society in which they lived. It was as if they first ‘taped together’ the home and then the world began to take care of itself.” (Douglas E. Brinley & Daniel K Judd, Eternal Families, “The Parent’s Role”)
"Corianton’s sins were grievous. And yet we have every reason to believe that Alma’s preaching touched the soul of his errant son, that Corianton ‘crossed himself’ (see Alma 39:9), repented, and returned to the ministry…
“Elder Orson F. Whitney held out this hope for the parents of wandering or wayward children: ’You parents of the wilful and the wayward: Don’t give them up. Don’t cast them off. They are not utterly lost. The shepherd will find his sheep. They were his before they were yours- long before he entrusted them to your care; and you cannot begin to love them as he loves them. They have but strayed in ignorance from the Path of Right, and God is merciful to ignorance. Only the fulness of knowledge brings the fulness of accountability. Our Heavenly Father is far more merciful, infinitely more charitable, than even the best of his servants, and the Everlasting Gospel is mightier in power to save than our narrow finite minds can comprehend.’ (CR, April 1929, p. 110.)” (McConkie & Millet, Doctrinal Commentary on the Book of Mormon, vol. 3, p. 320)