परित्राणाय साधूनां विनाशाय च दुष्कृताम्।
धर्मसंस्थापनार्थाय संभवामि युगे युगे।।4.8।।
4.8 For the protection of the pious, the destruction of the evil-doers, and establishing virtue, I manifest Myself in every age.
4.8 The good are those who follow the Dharma, as defined above. They are the foremost among the Vaisnavas, who have taken refuge in Me. While My name, acts and form are inaccessible to speech and thought, these devotees cannot get support, sustenance etc., for themselves without perceiving Me. They regard even a moments time without Me as a thousand Kalpas. They become broken in every limb because of the separation from Me. So I am born from age to age in the forms of gods, men etc., for protecting them by affording them the opportunity to behold My form and acts and to converse with Me. I am born also for the destruction of those who are opposed to such devotees and for the restoration of declining Vedic Dharma, which consists of My worship. The main purpose of incarnation is the revealing of His adorable form, so that all may worship Him. The destruction of the wicked is secondary only. There is no specific restrictions of the Yugas like Krta, Treta etc., for the appearance of Divine Incarnations.
Paritraanaaya saadhoonaam vinaashaaya cha dushkritaam; Dharma samsthaapanaarthaaya sambhavaami yuge yuge.
paritrāṇāya—to protect; sādhūnām—the righteous; vināśhāya—to annihilate; cha—and; duṣhkṛitām—the wicked; dharma—the eternal religion; sansthāpana-arthāya—to reestablish; sambhavāmi—I appear; yuge yuge—age after age