To not reciprocate in help and morever to be ungrateful is a single sinful activity. To be rejected by saints and moreover to be shameless, that is, not atone [for his sins] is a single sinful activity.¹

NOTE. Śrīmad-Bhāgavatam 6.1.7-8 describe atonement as follows.

na ced ihaivāpacitiṁ yathāṁhasaḥ
kṛtasya kuryān mana-ukta-pāṇibhiḥ

dhruvaṁ sa vai pretya narakān upaiti
ye kīrtitā me bhavatas tigma-yātanāḥ

“My dear King, if before one’s next death whatever impious acts one has performed in this life with his mind, words and body are not counteracted through proper atonement according to the description of the Manu-saṁhitā and other dharma-śāstras, one will certainly enter the hellish planets after death and undergo terrible suffering, as I have previously described to you.”

Śrīla Prabhupāda notes the following in his comment:

For karma-kāṇḍa there are twenty authorized scriptures, such as Manu-saṁhitā, which are known as dharma-śāstras. In these scriptures one is advised to counteract his sinful acts by performing other types of fruitive action. This was the path first recommended by Śukadeva Gosvāmī to Mahārāja Parīkṣit, and actually it is a fact that one who does not take to devotional service must follow the decision of these scriptures by performing pious acts to counteract his impious acts. This is known as atonement.

tasmāt puraivāśv iha pāpa-niṣkṛtau
yateta mṛtyor avipadyatātmanā
doṣasya dṛṣṭvā guru-lāghavaṁ yathā
bhiṣak cikitseta rujāṁ nidānavit

“Therefore, before one’s next death comes, as long as one’s body is strong enough, one should quickly adopt the process of atonement according to śāstra; otherwise one’s time will be lost, and the reactions of his sins will increase. As an expert physician diagnoses and treats a disease according to its gravity, one should undergo atonement according to the severity of one’s sins.”

Śrīla Prabhupāda’s comment on this verse is as follows:

The dharma-śāstras like the Manu-saṁhitā prescribe that a man who has committed murder should be hanged and his own life sacrificed in atonement. Previously this system was followed all over the world, but since people are becoming atheists, they are stopping capital punishment. This is not wise. Herein it is said that a physician who knows how to diagnose a disease prescribes medicine accordingly. If the disease is very serious, the medicine must be strong. The weight of a murderer’s sin is very great, and therefore according to Manu-saṁhitā a murderer must be killed. By killing a murderer the government shows mercy to him because if a murderer is not killed in this life, he will be killed and forced to suffer many times in future lives. Since people do not know about the next life and the intricate workings of nature, they manufacture their own laws, but they should properly consult the established injunctions of the śāstras and act accordingly. In India even today the Hindu community often takes advice from expert scholars regarding how to counteract sinful activities. In Christianity also there is a process of confession and atonement. Therefore atonement is required, and atonement must be undergone according to the gravity of one’s sinful acts.

Therefore, it is clear that if one does not engage in atonement according to the Dharma-śāstras, a person who has committed sinful activities and who has not taken to the path of surrender unto the Supreme Personality of Godhead will certainly be taken to hell for punishment.