As usual in general weekends I was reading Shrimad Bhagawat Gita yesterday night, in which verses were,
Smoham Sarvabhuteshu
Means I am equally disposed to all living entities
Means in any religion's person Lord is also in them too.
Most famous verses
Yada yada hi dharmasya, Dharma samsthapanayay Sambhavami Yuge Yuge....
Means to establish Dharma I(Lord Vishnu) appear millennium after millennium and I(Lord Vishnu) manifest myself(Supreme soul) personally
Lord also said that to establish righteousness, that is only my duty.
When Great Sadguru Lord Dattatreya
was asked how GOD do their work even though they are not residing on earth,
Lord said, GOD always make people "Neemitta" even though Lord appear as avatar or not like sage Atri
and mother Ansuya
was "Neemitta" for Lord Dattatrya's incarnation.
In dattabavani we say
Atransuya kare Neemitta, pragatyo jaga karan nischita
Isn't is Lord Vishnu's own will, to make honorable Jesus Christ , Budhdha, Guru Nanak and Muhammad, "Nemitta" to establish righteousness in the form of other religions?
"Neemitta" means we think we are doing, but it is GOD who is just doing everything, we are just eyes,nose and mouth of existence. Lord is in all beings, he is doing all that.
Why Jesus Ishu Christ, Guru Nanak, Lord Budhdha and Muhammad Payagambar should not be considered as Lord Vishnu's avatars?
I strongly believe that these all are Lord himself, because only he can establish religion and millions of people will follow him.
Great work like establishing Dharma can only be done by great soul only.
Just because hinduism scriptures have not been updated, so we should deny Lord's such avatars? This is unfair.
Lord himself said in Gita.
Following each his own activity, a man reaches perfection.
Yes Lord's intention is, Even though I am birth less, even though I reside on earth or not, whatever happens is my will only. I am the one who is operator. You can find me in any form on earth.
In Gujarati we have one tale,
Without God's will even leaf doesn't move.
So all those people who established righteousness in some way are Lord's avatars only, because only he can establish Dharma.
If we just follow whatever Lord said, of course we have to believe that they all are either Lord's avatars only. If someone deny then these people are Lord's dearest children than us otherwise who would be chosen for such a great great work(Karma)?
Edit
Main question
My dear friend, We accepted just scriptures, we did not accept "What is written in scripture."
Even though God wants to give a message of "Love" by Jesus, People will say show us your chaturbhuja form or we will not follow what you are trying to establish... because your name is not in scriptures.. then what does it mean by saying "I am in all living entities?" :( I am very sad now.
Some one in mathematics will give you idea that "This is how it works", it will not give list of all possible sums.
All the scripture mentioned some x avatars of vishnu, some 24 some 10. Did they write
"Only and only this x are avatars? others are not? Even though they have done greater work than past avatars?"
Just think for a moment "Jesus Christ's greateness" .. how great great great work he has done, Do you think except Lord, someone can give a message of "Love"?
Except Lord Budhdha, who can give message and knowledge that can build a whole "religion"?
Śrīmad-Bhāgavatam 1.3.24 Translation Courtesy Anonymous
Then, in the beginning of Kali-yuga, the Lord will appear as Lord Buddha, the son of Añjana, in the province of Gayā, just for the purpose of deluding those who are envious of the faithful theist.
The question takes you to comparison, and you believe yes only Lord can establish religion. If you come to this you are on my side, otherwise I will read your view and will accept your view if you explain me what I am unable to understand.
or
"Except these x people, others can not become avatars?"
But after Krishna, no avatar is recorded, Because nobody recorded yet. Krishna himself told "How it works", he did not tell you who is next avatar.
Just understand accept what Krishna said and think.
Now give me answer "Why Jesus etc. are not Vishnu's avatars as per what knowledge is given by Lord himself?"
One Answer is : "These avatars are not in scriptures", except this? any other answers are there, which are based on the knowledge of scriptures that I shared?
I have nothing related to people's acceptance or belief, I want to find some clause from sacred text of Hinduism that states "X person can not be avatar" or something that defines "What is avatar", so we can get answer based on this 2 things.
The cited two links from comments shows "What Ishu and Budhdha told?" , I am not interested in checking they are avatars or not based on what they said, I am finding according to Hinduism texts, What we should think about hem. They are not my subject, their life style and work we all know, We are judging our Gita's text or some other Hindu text vs this question.
I hope I made you clear about my view of question. We are not interested in people, or their belief, we are just analyzing our Gita knowledge which is ultimate.