Proving the basics of faith which are called in Arabic, Usul al-Deen
is very simple for every human being who uses his senses.

Main Facts of this existence are:
    1.    Tawheed which means that the existence came because it was created and the Creator is the most powerful and the most
knowledgeable and the most merciful and this is what we believe in it
as the main fact that the Creator who created the universe is One
because we see the whole universe from the smallest nucleus to the
biggest galaxy made of the same system - the movement in all the
universe is anti-clockwise. The whole universe, in every part of it,
gives unanimous evidence that the creator of the whole universe is
one.

If there was another creator apart from Allah SWT, we should have seen
any message from him as Ameerul Mo’menneen Ali (AS) said to his son :
“O son, if your Lord had a partner, you should have received any
message from that partner.

There are unlimited evidences about Tawheed that the Creator is one
but we mention very brief and very simple evidence, otherwise everyone
in his own thinking can reach to the fact that the whole universe was
created either by itself which is impossible or by a creator which is
the fact and the creator is one, Allah SWT.

    2.    The evidence of Nubowwat (Prophethood) is also very clear in the mind
of sensible persons that the Creator who created us knows our abilities and our limited knowledge and knows that we need to be guided by divine leaders who have full knowledge from Him, and the human being cannot run his life without guidance
from Allah SWT and Allah SWT guided us in two ways - one way is
through our intellect which is the inner evidence and the second which
is the outer guidance which came from Allah SWT to all human beings
through the messengers, prophets and their divine successors.

    3.    The faith in the justice of Allah SWT, Adl, is simply clear for
sensible persons because no one commits injustice but either because
of ignorance or because of need. Those who are ignorant or those who
feel need try to do injustices but Allah SWT is away from these
reasons and Allah SWT is the absolute needless and the All-knowing. It is out
of question in fact, to think that Allah SWT needs to do injustice on
anyone.

    4.    The faith in the Day of Judgement (Qiyamat) is also part of our basic
faith, Usul al-Deen because we as human beings believe that every good
or bad must have a result and the Day of Judgement is the final day in
which everyone will meet the result of his deeds. No human being can
believe that the Most Merciful Creator Allah SWT who is the Most Just
leaves everyone doing whatever they do without Day of Judgement. Day
of Judgement is part and parcel of the justice and mercy of Allah SWT.

    5.    We also believe in the Divine leadership after the Holy Prophet (SAWA)
i.e.Imamate,  because Allah SWt who knows the need of all human beings
to be guided by the prophets, He sent all the prophets to guide the
human beings and when He sent the last and greatest and final Prophet
Muhammad (SAWA) He ordered him to inform the Muslims in all the times
that his successors wil be Ameerul Mo’mineen Ali (AS) who is the first of twelve infallible Imams who will always guide the people to the right part of Allah SWT and the Holy Prophet
(SAWA).

Wassalam.