Divine Justice

Allah knows best how to weigh all aspects of a person's nature, intentions, capability, understanding, opportunities, knowledge, weaknesses and so forth. So, in the next life, Allah will judge absolutely justly, and no one will look at how Allah judges in the next life and say that Allah has been unfair. We will also understand better why people are judged as they are, since sometimes a small action may lead a person to jannah and someone who seems good on the surface may end up in the other place. 

However, having genuine wilayah (allegiance) to the Imams will, inshallah, aid a person in helping to attain a higher spiritual station, benefit from their intercession, and allow us to be with them in the next life. 

Most non-Shi'a today are not directly rejecting the Imams; rather, they are just following what they grew up with or what society says around them. This is different from someone who, for example, rejected Imam 'Ali (A) to his face. As is narrated from Imam Rida (A): "May Allah have mercy on the one who keeps our [teachings] alive... for if the people knew of the virtues of what we say, they would have followed us."

It is important not to be arrogant in one's faith, since even if a person believes in the Imamate, they may still suffer from misconceptions about what is true and be informed in the next world about those things that they thought were correct, which were not. Inshallah Allah would also be merciful about that. However, we can, God willing, pray that Allah guides us to what is most true. 

Qur'an 2:7 says: "Allah has set a seal upon their hearts and upon their hearing, and there is a covering over their eyes"

This refers to the loss of the ability to perceive the truth, especially about matters of the divine, truth, or right and wrong. (It does not refer to physical seeing and hearing, but rather seeing and hearing as metaphorical faculties for understanding. Similarly, the heart here is understood as a spiritual organ which perceives the truth.)

Although the verse attributes the sealing of the heart and ears to Allah, it is generally understood to mean that human beings bring this upon themselves through repeated transgression and obduracy against the truth, or denying the truth for personal gain. For instance, in the time of the Prophet (S), some of his enemies were trying to kill him or torturing the Muslims. Over time, this eats away at the capability of the heart (or other faculties) to perceive the truth, until it becomes blocked.

The verse does not specify who is covering their eyes, only that they are covered, and this suggests that they themselves are drawing blinders over their ability to perceive. (In the time of the Prophet (S), some people did this directly - for instance, plugging their ears when around the Prophet (S); today, some people do this by intentionally only going to media websites which reflect their views and ideologies and refusing to consider that they could be wrong.)

Some people who hold there is a reality to deeds in the unseen world would say that the performance of certain transgressions leaves an impact on the spiritual heart - that is to say, people plug up their hearts (ears, etc) through wrong deeds, just like one might plug up a drain over a long time through running detritus through it and not cleaning it out (through repentance and good acts). 

So it is a matter of cause and effect, or action and reaction, based on our own free will. 

However, Allah is the ultimate doer of all acts and all chains of cause and effect ultimately go back to Allah since Allah is the ultimate power in the universe. Furthermore, all things happen with Allah's permission and within the framework of what the divine decree allows, as well as the physical and spiritual laws of the universe. So for these reasons, the sealing is attributed to Allah. 

As for whether Allah intends for all of us to go to heaven... as one of the few creatures around us with free will, heaven and hell are possibilities for all of us, although we can be certain of Allah's justice, and hope for Allah's mercy and the intercession of the Prophet (S) and awliya (A).

I will leave this for someone else to answer fully but I just wanted to point out that the grass is always greener on the other side, sometimes some people seem to be enjoying themselves a lot or to "have it all" but in fact they are very unhappy. For instance, there are some people who are exceedingly rich but suffer from drug addiction, loneliness, family breakdown, etc. Does their wealth help them to avoid suffering from poverty? Certainly. Does it bring them full happiness beyond that? Not in and of itself; once a person's basic needs are met, happiness comes from other things. 

There are "religious" people who are happy, "religious" people who are unhappy, non-religious people who are happy, non-religious people who are unhappy, etc. It is true that the Muslim world is having a particularly difficult time these days (due to the global economic/political arrangement) but this is something new and not the same throughout time relating to being religious or not. 

While it is certainly possible for a practising Muslim to be in a very difficult situation, at least, adhering to shariah will help avoid certain things that can make life worse, such as suffering from alcoholism (inshallah at least it is avoided). Also, faith is usually a resource that people draw on in times of difficulty. 

Also it is true that it can be difficult to be a minority, and so being a practising Muslim in a country where you are a minority can add certain stresses, at the same time there are usually some advantages you get from that that others lack even if it seems like everyone else is having an easier time because they don't have to worry about prejudice, etc. 

Also there is a difference between being religious in name versus in ethics and principles. Some people call themselves "religious" because they do the outer aspects of Islam (such as reciting prayers on time or fasting) but they do not embrace the ethics and ideals of the Prophet (S), such as kindness, compassion, generosity, humility, forgiveness, standing up for justice, contributing to society, bravery, etc. Generally those values are what make individuals and the people around them happy. Of course one should embrace both the outer aspects of Islam and the ethical or inner aspects. 

As for complaining to Allah... it doesn't affect Allah if we complain to Allah. Even if, say, you are fishing and not catching enough fish, and you stand in front of the ocean and complain to the ocean, it doesn't affect the ocean, because the ocean is giant and you are not. And Allah is vaster than the ocean. However it is not healthy for ourselves to be angry at Allah for a long time. Still it is fine and even good to tell Allah that you are having a difficult time or are in pain or are suffering or feel lack and in need of a change. Sometimes Allah just wants us to ask!

Anyway everyone goes through hard times, particularly right now a lot of people are going through tough times, I hope things get better for you if you are having a difficult time. After every winter, there is a spring!

The hardships and tests we face - God willing - refine us not only as human beings but increase our spiritual understanding and capacity to behold the divine. This is one reason why human being agreed to accept the responsibility of free will - with it comes a risk (hellfire) but also great potential.

Ideally the main goal of the material existence (as I understand it) is for human beings to deepen their inherent spiritual understanding as much as possible. A child and an adult may both go to jannah; however, depending on their experiences (as not everyone grows throughout a long lifespan), they may end up with a different inherent capacity to perceive the divine there. (One might equate that with "higher in jennah")