B.G 4.07 and 08
yadā yadā hi dharmasya glānirbhavati bhārata। abhyutthānamadharmasya tadātmānaṁ sr̥jāmyaham ॥7॥
O Arjuna, certainly I manifest myself as and when there is detorioration of righteousness and rise of injustice.
paritrāṇāya sādhūnāṁ vināśāya ca duṣkr̥tām। dharmasaṁsthāpanārthāya sambhavāmi yugē yugē ॥8॥
I manifest time and again for protecting the virtuous, for the destruction of the evildoers, and for the establishment of the righteousness.
Gīta Bhāshya 4.07 and 08
There is no rule that the Lord must perform protection and such activities only after taking birth. Even then, for play, because of His inherent nature, He behaves accordingly.
na janmanaiva paritrāṇādikaṁ kāryam iti niyamaḥ। tathāpi līlayā svabhāvēna ca yathēṣṭacārī। tathāhi uktam–
There is no rule that the Lord must perform protection and such activities only after taking birth. Even then, for play, because of his inherent nature, He behaves accordingly. Therefore, it is said:
"dēvasyaiṣa svabhāvō'yam।"
"This wish of the Lord is because of His inherent nature."
"lōkavattu līlākaivalyam।"
"Just like those who sport in the world, for its benevolance."
"krīḍatō bālakasyēva cēṣṭāṁ tasya niśāmaya।"
"Understand that He sports, as if like a child, with His playful activities."
"aribhayādiva svayaṁ purādvyavātsīdyadanantavīryaḥ।"
"That lord with limitless power left the city Himself, as if He fears the enemy."
"pūrṇō'yamasyātra na kiñcidāpyaṁ tathāpi sarvāḥ kurutē pravr̥ttīḥ। atō viruddhēṣumimaṁ vadanti parāvarajñā munayaḥ praśāntāḥ॥"
"He is complete all the time and has nothing to accomplish. Even then, he engages in intentioned activities. Hence, the wise sages who have tranquillity, in both the transcendent and the immanent, say - 'Contradictory are His activities'."
ityādi rugvēdakhilēṣu ॥8॥
-such testimonials are from Rigvēdākhila.