greetings comrade ,
As an Indian , iam confused as to why iran supports a Christian Armenia instead of islam Azerbaijan .
Don't take this question , as if iam trolling , i know about historical and cultural affinity between Armenia and iran .
I wanted to know an Iranians perspective in this regard
Actually it doesn't. Iran sent the IRGC to train troops from the Republic of Azarbaijan during the first Karabakh war. More than 10 Iranian military personnel fell as martyrs in Azarbaijan, there are even videos of them present on the frontlines. You can ask user Muhammed45 to direct you to one, since he posted it here before. There is also a speech by an IRGC commander who was gifted a dagger by Heydar Aliyev in person for his engagement.
What then happened, however, is that the Baku regime spit in Iran's face so to say, by flirting with separatist tendencies against Iranian territorial integrity. So Iran decided to play a mediating role between the two sides in the Karabakh conflict, and to remain neutral.
Things worsened when the Arrani regime (so-called Republic of Azarbaijan) not only sealed a strategic alliance with the zionist regime, becoming one of the largest importers of Isra"el"i-made arms, but according to reports even allowed Mossad to use its soil to conduct UAV spying missions over Iran, and to recruit terrorists for the assassination of Iranian nuclear scientists.
Baku's missteps were further compounded by Erdogan's speech at the recent victory parade in Baku, where Turkey's president expressed the notion that Baku has designs on sovereign Iranian lands.
Another issue blurring things is that the current Armenian administration, brought to power by a CIA-sponsored "colored revolution" a couple of years ago, is in fact zionist, much like the treasonous Aliyev regime of Baku. Hence Iran has no incentive to support it, despite Baku's brazen hostile actions. Some in Iran even suspect that the Pashinyan regime is covertly on board with Tel Aviv, Baku and Ankara in sabotaging Armenia's defensive power and thereby indirectly helping the Arranis seize territory.
Recurrent allegations of Iranian military intervention on Armenia's behalf in the mainstream and regional media represent propaganda for which no proof was presented to date. Media from Turkey and Arran, as well as from the west are spreading this claim in order to whip up hostility against Islamic Iran amongst not just Turkey's and Arran's populations, but also - so they hope, among Azari Iranians susceptible to pan-Turkist propaganda. In this regard, the zionist regime and its operatives (including some key academics who authored books to this effect and have been advising Baku authorities) have been at the forefront of attempts to cultivate separatist sentiments among Azari speakers of Iran, but largely in vain. Despite all these efforts, separatists and pan-Turkists do not represent more than a tiny fraction of Azari Iranians, who historically have been some of the staunchest Iranian patriots and nationalists, aware of their Iranian (much rather than Turkic) ethnic roots as well as of their shared Iranian culture (the name Azarbaijan or Azarbadegan as it was originally called, is itself genuinely Iranian and not Turkish).
Nonetheless, the enemy has been more or less able to contribute to the appearance of an identitarian, culturally centrifugal lobby of sorts comprising a limited number of Iranian politicians (essentially local ones and members of Majles, Iran's parliament, as well as some civil servants) claiming to represent Azari Iranians, who strive for ethnic federalization of the Islamic Republic, in line with their separatist counterparts in the exiled opposition. Needless to say, such a restructuring of the state would represent a dangerous stepping stone towards the balkanization and dismantling of Iran.
But there's one central factor which dooms to failure all these ethno-separatist, NATO- and zionist-masterminded plots against Iran: the simple fact that owing to urbanization, social modernization, the development of infrastructures and their corollary ie intermarriage, as well as the generalization of the national language, Persian, a significant majority of Iranians actually descend from several and not just one single sub-national linguistic group, ie most Iranians are of mixed linguistic backgrounds and can impossibly be compartmentalized into a so-called "ethnic" category.
One last point to add to this brief overview is that the Islamic Republic too has its allies and supporters across the river Aras. These essentially consist of religious elements of Baku society, and they adhere to the Islamic revolutionary ideology of Imam Khomeini (r.a.). Ever since Iran lost the southern Caucasus to the Russian empire in the first half of the 19th century, religion has lost much of its relevance over there though, as a result not just of 70 years of Soviet communism, but also of the Aliyev regime's ultra-secularist policies, complete with hijab bans at certain public places, the jailing of clerics critical of the regime's religious policies, economic corruption and alliance with Israel. This of course is in stark contrast with Baku's Turkish ally Erdogan. Along with this, Baku proceeded with the installment of a number of wahhabi preachers and mosques as a means to counter-act and contain any possible Shia Islamic political and religious revival. Much like the Aliyev regime authorized Turkey to ship over and station right next to the border with Iran some of its Syrian insurgent proxies (terrorist mercenaries of anti-Shia "jihadist" persuasion). Iran's IRGC for its part helped set up and trained a unit of fighters from the Republic of Azarbaijan, the Hüseynciler or Hosseynioun Brigade, which served in Syria as part of the loyalist camp supportive of the government in Damascus.
Now the thing is that these pro-Iranian movements and groups in Arran are at the same time patriotic Azaris who do not see eye to eye with Armenia over Karabakh, even while they oppose the ruling regime in Baku. So Iran's retort to Baku's backstabbing and provocations has not so much consisted in taking sides with Armenia in the Karabakh conflict, but in promoting Iran-friendly Islamic oriented local currents.
This being said, a new red line for Iran is the Zangezur corridor which, if wrested away from Armenia by Baku's forces and their allies, would completely cut Iran off from Armenia, jeopardizing not just Iran's North-South transport corridor from the Persian Gulf to Russia, but also increasing future threats of zionist and takfiri terrorist encroachment on Iran's northwestern borders as well as enhanced separatist agitation. Hence Iran made it clear that while it supports Baku's legally sound claims to Karabakh, it will not allow other recognized international borders in the area to be altered by force. To this effect, Iran staged a massive wargame in the border zones and sent a clear message to Baku and Turkey that it will intervene in case they tried to unlawfully snatch land from Armenia proper.
Hope this helps!