Why do we need Yamalokam?

Question

Given that Karma and punarjanma (rebirth) are the prime beliefs of Hinduism, why do we need Yamalokam and punishment in it?

I mean, through Karma, the fruits of both good and bad deeds are obtained either in the same birth or the next one. Then why do we need Yamalokam?

Answer 1

The answer to this question is linked to the concept of residual karma. This residual karma idea and what happens to evil-doers is explained in Brahma Sutra.

But of others (i.e. those who have not performed sacrifices etc.) the ascent is to the abode of Yama, and after having experienced (the results of their evil works) the descent (to the earth again takes place). On account of such a passage (for the evil-doer) being declared by the Sruti. (Brahma Sutra Sankara Bhasya 3.1.13)

The Sruti passage referred to in the above shloka is:

The Hereafter never reveals itself to a person devoid of discrimination, heedless, and perplexed by the delusion of wealth. "This world alone exists," he thinks," and there is no other." Again and again he comes under my sway. (Yama speaks in Katha Upanishad I.2.6)

It is clear that if you do bad deeds that you end up in Yama Loka. However, there are two perplexing questions here. Does the person who descends to earth from Yama loka return with any Karma (i.e. is the Karma of the evil-doer after serving his term in Yama loka zero?)? What decides that a person will after death be immediately reborn in earth or return to earth after serving a time in Yama loka? These two questions are actually linked. The answer to this question is given in Brahma Sutra:

On the exhaustion of (good) work (the soul) with residual Karma (descends to this earth), as is known from the Sruti amd Smriti, along the path (it) went by (from here) and differently too. (Brahma Sutra Sankara Bhasya 3.1.8)

The above Sutra says that what is exhausted in heaven is only that specific Karma which gave the soul a birth in lower heaven, but on the exhaustion of this Karma the remaining Karma, good and bad, brings it back to earth. While this Sutra talks of heaven and good deed, it also applies to Yama Loka and bad deeds. Let me explain the idea by a concrete example. Let us suppose that a dead person has a list of 10 karmas with goodness values (1, -3, 4, 5, -100, 4, 3, 2, 5, 8) where the minus sign stands for evil deeds. What Brahma Sutra Sankara Bhasya 3.1.8 is saying is that this person will go to Yama Loka only for that extremely evil deed of goodness value -100. After he has exhausted the bad effect due to the -100 Karma, he can then go back to earth with the residual karma (1, -3, 4,5,4,3,2,5,8). The idea is that only extremely evil or good deeds lead a man to Yama loka or to lower heavens. All minor good and bad karmas are served on the earth plane.

Answer 2

It is not necessarily that one only experiences his karma in this life or the next one. For example, there are numerous references in the Puranas (Padma, Skanda, etc) that state that for a particular action, one will have to take birth as a dog for 100 lives. So the actions have the power to act in many lives going forward.

To answer this question fully, it is important to understand karma:

It is stated in the Padma Purāṇa that there are four kinds of effects due to sinful activities, which are listed as follows: (1) the effect which is not yet fructified, (2) the effect which is lying as seed, (3) the effect which is already mature and (4) the effect which is almost mature. It is also stated that all these four effects become immediately vanquished for those who surrender unto the Supreme Personality of Godhead, Viṣṇu, and become engaged in His devotional service in full Kṛṣṇa consciousness (1.1.24)

Those effects described as "almost mature" refer to the distress from which one is suffering at present, and the effects "lying as seed" are in the core of the heart, where there is a certain stock of sinful desires which are like seeds. The Sanskrit word kūṭam means that they are almost ready to produce the seed, or the effect of the seed. "An immature effect" refers to the case where the seedling has not begun. From this statement of Padma Purāṇa it is understood that material contamination is very subtle. Its beginning, its fruition and results, and how one suffers such results in the form of distress, are part of a great chain. When one catches some disease, it is often very difficult to ascertain the cause of the disease, where it originated and how it is maturing. The suffering of a disease, however, does not appear all of a sudden.

(Source: The Nectar of Devotion -- Vrndavana, November 6, 1972)

So the conclusion is that is extremely difficult to understand what actions we are suffering for currently and what the future will entail. You can see that Padma Purana also mentions devotional service to Visnu as a solution.

In Srimad Bhagavatam Canto 3, Lord Kapila explains to his mother Devahuti about the path of the conditioned soul in the material world. See in particular Chapter 30 and Chapter 31. From this it appears that the soul must sometimes have his subtle body covered in order to suffer extreme pain on account of his previous sinful reactions. You can think of it in this way: if you are very pious, you can go to the heavenly planets, Svargaloka. The enjoyment there cannot be copied on this earth planet. Similarly, some of the punishment can not be carried out on this earth planet either. But as karma and Yamaraja are unfailingly fair and just, the punishment must be meted out.

On an interesting side note, the concept of hell does not have an evil ruler, as it does in such religions as Christianity and it is also not eternal. Yamaraja is actually a pure devotee of Lord Visnu and he has the utmost compassion for all souls, considering his job a thankless task and to be his service to the Supreme Lord to reform the wayward living entities in the material world. See Srimad Bhagavatam Canto 6 for more info.

Answer 3

The simple answer is, for getting punishment of the committed sins.

But then the question becomes, as you have raised, why someone would experience the results in hell when he has to also experience the results of his bad actions on earth itself? This is a nice question. It is known as the problem of double retribution. To understand the reason of why or why not, we have to first understand what causes a sin.

For smooth and proper operation of life here and in the hereafter the rishis formulated various laws. Through their power gained through austerity they could perceive past, present and the future, so they knew what activities lead to what conclusions. They were aware of which activities break the order and what could be done to mend the order. Through various Puranas and scriptures they they gave out these laws for the benefit of the humans. So whenever any set law of the sages (varnashrama dharama etc.)is violated, it creates a sin. And for breaking the order or the rule one goes to Naraka for punishment:

varṇāśramaviruddhaṃ ca karma kurvanti ye narāḥ
karmaṇā manasā bācā nirayeṣu patantite [VP - 2.6.32]

Meaning
He who through his mind, speech and action does work that is against his varnashrama dharma (duites as per his caste) falls into hell.

However, sometimes a law may get violated unintentionally or out of necessity. So as a counter action, the sages have also stated the actions that should be done in such cases. The set of actions done for the expiation of sins is known as prayaschit.

Sages prescribe a penance for unintentionally committed sins. Some declare, on the evidence of the revealed texts, (that it may be performed) even for an intentional (offence). [Manu. Smrt. - 11.45]

Apart from other bad actions, some grave acts like (murder of Brahmin, mating with someone forbidden by the scriptures, drinking alchol etc.) when done consciously has no other expiation than death. So here on earth itself one can free himself of sins by proper expiation. If however, on committing the sins, one doesn't expiate for them on earth, then he has to experience the corresponding punishment in hell as mentioned in various scriptures:

pāpakṛdhyāti narakaṃ prāyaścittaparāṅmukha: [VP - 2.6.38]
He who commiting a sin who doesn't want to expiate, goes to naraka (hell)

So the result of certain grave actions are not experienced on earth but in other planes of existence like hell and heaven. It's because they can not yield equivalent result here on earth. For example, when one performs 100 asvamedha yajnas then the resulting merit becomes so big that he can't enjoy it here on earth. So he has to become the king of heaven. Similarly certain bad actions and severe actions like murder of people are so grave that they can't have equivalent effect here. So for getting equivalent punishment they have to go to hell. Only the result of minor good and bad actions are experienced here.

REFERENCE:
Mahabharat Apaddharmanusasana Parva, Chapter 165
For an overall idea refer Garuda Puran, Agni Puran, etc.