Vaali sugreeva were brothers . Vaali was incarnation of Indra , Sugreeva ,of Surya. Sugreeva sought help of Rama to finish Vaali. After tests by Sugreeva ,Rama sent Sugreeva to Fight Vaali.
- Fisrt time HE did not kill Vaali.
- Sugreeva came back .
- Rama assured to kill ,put a garland to him.
- Vali was killed from behind by Rama.
- why did Rama not kill him first time ?
Rama is God ,therefore thinking he did not recognise Vaali ,is untenable. When two brothers are at loggerheads ,they usually go to any extent in fight. But once revenge is over , There is sudden surge of brotherhood . and subsequent repentance[this is the nature of blood relation].Thus one must never interfere in a brotherly squabble.Chances are they unite and treat you as an outsider and even abuse you for instigating enmity.One must always give a chance to such reversal of mindset.
Rama spared Vali for the first time to bring such reversal of mindset towards his brother.
2. Why did he kill Vaali?
Vali had taken away wealth ,wife and belongings of his brother without any fault of his. So he was liable for punishment. Ram was a Kshatriya Chakravarti King and he had moral right [as a duty] to end Vaali's life .
3. Why did he kill from behind and not in a straight war.
what Vali had done ,renders him into the category of Mrugas[animals] , Kings don't wage war against animals , they hunt them or kill them as a disturbance for forest life.
Vali was Indra , he had natural Bhakti towards Rama , more than Sugreeva. Had Rama befronted him, he would have immediately asked forgivance and Rama would be compelled to leave him alive.
But crime of Vali was he had taken birth to serve Rama and in the flow of arrogance of power and might due to boons and strength , he forgot his duty [purpose of Birth] and befriended Ravana. Also he hurt Sugreeva [a devotee] , More importantly He was standing in a camp against Hanuman. Sugreeva on the contrary had befriended Hanuman and was under his guidance.
God only sides with the one who sides with Hanuman[Vayu]. HE does not prefer to see the face of those who go against Hanuman, even if they are his devotees]. [thus he kills Vali from behind to show going against Hanuman is unpardonable ].
[same Vali becomes Arjuna and sides with Bheema , Sugreeva becomes Karna goes against Bheema] Krishna ignores Karna and takes Arjuna very close.
Those who pray Lord Vishnu without Praying Vayu [hanuman] , God does not give any fruits ,however hard and devotionally one prays ,its of no use . God does not appear before them [like vali] and finishes them off from behind.
If you Pray Hanuman along with Vishnu only then you get your wishes fulfilled like Sugreeva and Arjuna].
Lord's arrows are nothing but Vayu himself. When Arrows pierce heart of Vali[ Vayu enters his heart] , he gets knowledge , asks forgiveness to lord and Rama offers to give him back his life. But Vali refuses because he does not want to let go the chance of dying in the hands of Rama [which ensures Moksha].
Thus Vaali surrenders all his beloved things to the lords' feet according to the dictum " daraan sutaan priyaan ....nivedayet...."
This is what is known as Srikrishnarpanamastu .