The most important principles of ISLAM are:
1: Monotheism
2: Prophecy
3: Resurrection
4: Justice
5: Imamat
Monotheism:
A Muslim(who believes in ISLAM) must beleive and give testimony to the oneness of GOD.
Muslims believe that the only creator of this world is GOD and HE is alone.
HE has no father, no mother, no wife and no child. HE is the one.
Prophecy:
When GOD created humankind, HE had not finished his kindness to the humankind.
HE sent his help with his prophets, GOD has sent over 124,000 prophets in different ages.
But only 5 of them have books sent by GOD, they are 'Nooh' , 'Ibrahim' , 'Moosa' , 'Eesa (Jesus Christ)' and 'Mohammad'.
Muslims must believe and give testimony that all the prophets are brought to help humankind live in the best way, get knowing GOD, himself and his environment and of course Mohammad is the last messenger of GOD and the great prophet of ISLAM.
Resurrection:
A muslim must believe that after his life and when he dies, he is not destroyed, and he will be alive again to explain what he has done in his life.
Actually humans rights are not violated and it's the real meaning of penalty and of course heaven and hell.
Justice:
Idea of ISLAM about justice is that all of the people from the first day of creation to the last day of this world's life have the same rights.
A muslim mustn't respect a man because he is rich or disrespect a man because of his poverty, he should respect both of them in a same way.
Imamat:
One of the great differences between ISLAM and other religions is this important point.
ISLAM is the last and most complete religion that GOD has sent, so that, it is not finished when the prophet is dead. But after the great prophet someone else that is approved by the prophet take the steering guidance of Muslims society.
Number of these men is 12.