Canto 2 -
Ayodhyā-kāṇḍa
Chapter 1: Daśaratha Desires to Appoint Rāma as the Crown Prince
Text 2.1.7

स हि देवैरुदीर्णस्य रावणस्य वधार्थिभिः।
अर्थितो मानुषे लोके जज्ञे विष्णुः सनातनः॥

sa hi devair udīrṇasya rāvaṇasya vadhārthibhiḥ
arthito mānuṣe loke jajñe viṣṇuḥ sanātanaḥ

saḥ = He; hi = indeed; devaiḥ = by the devas; udīrṇasya = of the passionate 1; rāvaṇasya = Rāvaṇa; vadha-arthibhiḥ = who sought the death; arthitaḥ = upon being beseeched; mānuṣe = of humans; loke = in the world; jajñe = who had taken birth; viṣṇuḥ = Lord Viṣṇu; sanātanaḥ = was the eternal.

Indeed, He was the eternal Lord Viṣṇu who had taken birth in the world of humans upon being beseeched by the devas who sought the death of the passionate Rāvaṇa.

How is it that Lord Rāmacandra is described as having more auspicious qualities than His brothers? That is because He is the primary incarnation of Lord Viṣṇu [among the four sons of Daśaratha].

Indeed, it is well known from the Śruti scriptures:

ajāyamāno bahudhā vijāyate

“The Supreme Being takes birth in many forms while remaining unborn.” (Taittirīya Āraṇyaka 3.12.13.8)

These devas had their own purposes—they were not the Lord’s pure devotees with no motive other than to please Him. Apart from that, they were quite conceited, with the attitudes expressed [in Bhagavad-gītā 16.14] as īśvaro ’ham ahaṁ bhogī siddho ’haṁ balavān sukhī, “I am the lord of everything. I am the enjoyer.  I am perfect, powerful and happy.” Indeed, the very word deva can etymologically refer to a proud person. These devas were the ones who prepared to go on war with Kṛṣṇa for the sake of a Pārijāta tree after He had accomplished their purposes by killing Narakāsura.

Udīrṇasya indicates that Rāvaṇa was in the process of destroying the entire world due to his natural pride. He threw the devas out of their residences [though] they had formerly favored him. The devas surrendered unto Lord Viṣṇu with the idea that when this person is destroyed, they would happily enjoy [their celestial] kingdom. And therefore they prayed to Lord Viṣṇu [for help]. They did not engage in meditative worship [of Lord Viṣṇu to engage in His eternal loving service in the spiritual world].

Mānuṣe loke. The Supreme Lord made Himself very accessible to the world of humans, the same world that is so intolerable and nauseating to the devas that even to accept sacrificial offerings from humans they keep themselves at a distance of one yojana [above the sacrificial arena].

He took birth in this world as Rāma; He did not just appear like Nṛsiṁha [from a pillar] and so on. In this world, birth is preceded by ten months of pregnancy. But our Lord spent twelve months in pregnancy.

Viṣṇuḥ indicates that He is all-pervading. He arranged for a situation wherein a person who is pervaded by Him considered Him to be His son.