Our edicts are based on the teachings of the Imams of the Ahlulbait (peace be upon them) through the narrations that reached us in reliable ways, which all Muslims are required to act upon. The Prophet (peace be upon him and his holy progeny) ordered the nation of Islam to refer to the Ahlulbait and follow them in the famous well-known narration that is reported by numerous ways in the books of Shias and Sunnis: "I leave among you the two weighty things: the Book of Allah and my progeny; as long as you follow both of them, you will never be misguided."
Acting upon this narration, as well as other similar narrations, to follow the AhlulBait is not obligatory on the Shias only, but it is an obligation on all Muslims.

The said person is not considered as disobedient, but is liable for proceeding to commit an act that he was informed to be a sin. An example of this is if a person drinks from a glass thinking it to be wine, but it turns out to be water.

Adalah – as a condition in the imam of the congregational prayer and in the witness – is a level of fearing Almighty Allah that leads to avoiding the committing of major sins. Committing small sins without insistence does not affect it.
Adalah – as a condition in the marja – is a high level of God-fearing which leads the person to refraining from disobeying the religious laws and committing sins – whether the sins are small or major. If on the rare occasion he commits a sin, he would rush to repent to Almighty Allah and seek his forgiveness.
A person who holds 'adālah is called "adil".

Yes, it is obligatory to follow the most knowledgeable Mujtahid.

When a person starts emulating a marja after he realizes his responsibility in observing the rulings of the Sharia, he refers to the basic logic that every sane person will arrive at, and upon which one will be responsible to act in accordance to.
There is no doubt that this logic obligates the ignorant to refer to the knowledgeable in what the latter knows.
As the knowledgeable in the religious sciences (i.e. the mujtahids) differ in their views in various religious rulings, including their view in following the most knowledgeable, it becomes necessary to follow the edicts of one of them based on a distinguished characteristic that others do not possess, which is being the most knowledgeable.
Although the views of some of the mujtahids do not necessitate following the most knowledgeable, but in order to assure that we fulfil our responsibility of observing the Sharia with certainty, the initial logical ruling leads to following the edicts of the most knowledgeable in the issue of referring to the most knowledgeable mujtahid. This is so because the view of mujtahids who do not necessitate following the most knowledgeable allow following the most knowledgeable. To the contrary, the views of those who necessitate following the most knowledgeable do not allow following any mujtahid other than the most knowledgeable.
In other words, following the most knowledgeable is obligatory according to some and permissible according to others, whereas not following the most knowledgeable is permissible according to some and prohibited according to others.
It is natural then to follow the most knowledgeable in this issue. If his view – in this issue – necessitates following the most knowledgeable, one should follow him in the rest of his views. If his view does not necessitate following the most knowledgeable, then one can follow another mujtahid.

It is obligatory on the individual to refer to the marja in learning about the religious rulings and implementing them in the matters of his worships, dealings, family relations and relations with other people, since the sharia has rulings and guidance for all issues that one could run into.
In other aspects of life, the marja is referred to as an advisor since he has knowledge on the Holy Quran and the teachings of the Ahlulbait (peace be upon them).

He should follow one of them because only one of them has the religious authority for the duty-bound person, even if he may not have initially identified him. The individual should determine this Marja in accordance with the rules of the Sharia, so that he may learn of the Islamic laws pertaining to the issues that he faces in the usual course of his life.

If one is aware that there are differences between the maraja's in the rulings that affect him, which is usually the case, then he must observe precaution. Since this is not practical for many to do so, he must find the most knowledgeable from them and follow him.

Religious adulthood is recognized for the male by any of the following three signs, whichever happen first:
1. The presence of hard hair on his face or in the pubic area.
2. The release of semen, whether it was during a wet dream or when awake.
3. The completion of fifteen lunar years.
The female reaches adulthood when she completes the age of nine lunar years.

A believer should aim to fulfill the religious responsibilities of upholding the orders of the Sharia; one of them is learning the Islamic laws and teaching them. This could be achieved by learning more about the religion – and not necessarily reaching the level of ijtihad – by which a believer could serve Islam. One could serve the religion and be a role model amongst his society, family and friends by being obedient to the Islamic laws and by spreading the religious teachings in the areas where he resides. Therefore, ijtihad is not a goal that a student should have from the beginning.
Ijtihad is a talent that can be achieved by studying and with the guidance of Almighty Allah. A student of Islamic studies should study hard and make use of his time as much as possible. If he achieves this, then he can thank Almighty Allah for this bounty. If he does not, he can still serve the religion.

You should follow the scholar who has reached the level of ijtihad and fulfills all the other conditions of the marja in all issues.
The derivation of the edicts from the religious sources require a great amount of knowledge and experience gained from continuous studying and research over many years. The authenticity of the traditions is only one factor taken into consideration in this process. Only the scholars who have reached the level of ijtihad have the capability to undertake this.

It is natural to have different derivations, as people differ in their understanding of a single text, whereas the mujtahids deal with numerous texts, plus the fact that as time passes further away from the time of the texts, fallacies and probabilities increase. From this, the mission of a mujtahid becomes harder and his responsibility becomes greater in protecting the religion in a correct way and to the greatest possible extent. The oppressors and the liars throughout the times have made obstacles for us in obtaining the truths from the Imams (peace be upon them) which made the mission of the mujtahids more difficult. Therefore some variations are to be expected, in all areas of jurisprudence.

The difference in deriving the laws between religious jurists naturally originates from their difference in understanding the religious texts or considering some of them over the others. His Eminence, Sayyid Al-Hakeem (may Allah prolong his life) sees that alcohol is najis, if it is an intoxicant and naturally liquid. Based on this, the prayer is invalid if the praying person’s body or clothes came in contact with it.

If the layperson acted upon the edicts of the qualified marja he is following, then Almighty Allah will excuse him if his marja was not correct.

It is obligatory to inform the misinformed person if the latter is expected to act upon it.

The individual – who has not reached the level of ijtihad, nor does he act on precaution between the edicts of the mujtahids – cannot guarantee the correctness of his deeds before Almighty Allah, unless they correspond to the edicts of a religious scholar who is an expert in Islamic jurisprudence, i.e. a mujtahid. Referring to the expert will relieve him from liability if the edicts of the mujtahid do not conform to the actual legislated laws of Allah Almighty. Without following the expert mujtahid, the person will be held responsible before The Almighty if the actions and transactions were not really in accordance to the religion.

You can change your marja by starting to refer to the edicts of the new marja and acting upon them.
However, the change is permissible only if it is based on religious evidence, for example, when it is proven to you that the new marja is more knowledgeable than the current one.

Yes, the testimony of the ahl-ul-khibrah is considered as religious evidence as long as it is based on referring to the researches of the mujtahids.

It is not permissible to switch from a mujtahid to another just because the second mujtahid's edict is easier to follow or pleases the individual more. The first marja must be followed as long as he is still fulfills all the conditions of the marja. However, if the marja that you are following has an obligatory precaution, then you can follow another qualified marja in that issue.

It is not permissible to change from the current marja unless it is proven by religious evidence that another mujtahid is more knowledgeable than him.