The conditioned soul has a false ego, and as a result of his karma he gets different types of bodies in this material world.
(Srimad Bhagavatam---4:11:25----purport).

Being very eager to enjoy the fruits of their activities, conditioned souls become involved in the actions and reactions of material life. Consequently they enjoy and suffer the results of karma.
(Sri Caitanya Caritamrta----2:15:179----purport).

This material nature is the separated energy of the Supreme Lord, and similarly the living entities are also the energy of the Supreme Lord, although they are not separated but eternally related. So the Lord, the living entity, material nature and time are all interrelated and are all eternal. However, the other item, karma, is not eternal. The effects of karma may be very old indeed. We are suffering or enjoying the results of our activities from time immemorial, but we can change the results of our karma, or our activity, and this change depends on the perfection of our knowledge.
(Bhagavad-Gita---introduction).

One who has taken birth in the land of Bhārata-varṣa has a full opportunity to study the direct instructions given by Kṛṣṇa in Bhagavad-gītā and thus finally decide what to do in his human form of life. One should certainly give up all other propositions and surrender to Kṛṣṇa. Kṛṣṇa will then immediately take charge and relieve one of the results of past sinful life (ahaṁ tvāṁ sarva-pāpebhyo mokṣayiṣyāmi mā śucaḥ (B.G.18:66). Therefore one should take to Kṛṣṇa consciousness, as Kṛṣṇa Himself recommends. Man-manā bhava mad-bhakto mad-yājī māṁ namaskuru: (B.G.18:65) "Always think of Me, become My devotee, worship Me and offer Me obeisances." This is very easy, even for a child. Why not take this path? One should try to follow the instructions of Kṛṣṇa exactly and thus become fully eligible to be promoted to the kingdom of God (tyaktvā dehaṁ punar janma naiti mām eti so'rjuna (B.G.4:9). One should go directly to Kṛṣṇa and engage in His service. This is the best opportunity offered to the inhabitants of Bhārata-varṣa. One who is fit to return home, back to Godhead, is no longer liable to the results of karma, good or bad.
(Srimad Bhagavatam---5:19:23----purport).

As stated in the Brahma-saṁhitā, karmāṇi nirdahati kintu ca bhakti-bhājām: (Bs. 5.54) one who has taken to Kṛṣṇa consciousness, devotional service, is not affected by the results of karma. In this verse, karma has been stressed on the basis of karma-mīmāṁsā philosophy, which says that one must act according to his karma and that a supreme controller must give the results of karma. The subtle laws of karma, which are controlled by the Supreme, cannot be understood by ordinary conditioned souls. Therefore Kṛṣṇa says that one who can understand Him and how He is acting, controlling everything by subtle laws, immediately becomes freed by His grace. That is the statement of Brahma-saṁhitā (karmāṇi nirdahati kintu ca bhakti-bhājām (Bs. 5.54)). One should take to devotional service without reservations and surrender everything to the supreme will of the Lord. That will make one happy in this life and the next.
(Srimad Bhagavatam---6:14:55----purport).

Śrīla Viśvanātha Cakravartī Ṭhākura says in this connection that one who has developed Kṛṣṇa consciousness and who exists in love with Kṛṣṇa is no longer subject to suffering and happiness under the laws of karma. Indeed, he is beyond karma. The Brahma-saṁhitā says, karmāṇi nirdahati kintu ca bhakti-bhājām: (Bs. 5.54) a devotee is free from the reactions of his karma because he has taken to devotional service. This same principle is confirmed in Bhagavad-gītā (14.26). Sa guṇān samatītyaitān brahma-bhūyāya kalpate: one who is engaged in devotional service has already been freed from the reactions of his material karma, and thus he immediately becomes brahma-bhūta (S.B.4:30:20), or transcendental. This is also expressed in Śrīmad-Bhāgavatam (1.2.21). Kṣīyante cāsya karmāṇi: before attaining the stage of love, one becomes free from all the results of karma.
(Srimad Bhagavatam---6:17:17----purport).

Simply by becoming a devotee, one is freed of all the reactions of karma. Similarly, simply by the desire of a devotee, a conditioned soul can attain liberation and transcend the results of karma. Since everyone can be liberated in this way, one may conclude that it is according to the sweet will of the devotee whether the material world exists or does not exist. Ultimately, however, it is not the sweet will of the devotee but the will of the Supreme Personality of Godhead, who, if He so desires, can completely annihilate the material creation. There is no loss on His part. The owner of millions of cows does not consider the loss of one she-goat. Similarly, Lord Kṛṣṇa is the proprietor of both the material and spiritual universes. The material world constitutes only one-fourth of His creative energy. If, according to the desire of the devotee, the Lord completely destroys the creation, He is so opulent that He will not mind the loss.
(Sri Caitanya Caritamrta----2:15:179----purport).