"Say: We believe in Allah (God Almighty) and that which was revealed to Abraham and Ishmael and Isaac and Jacob and the tribes and that which was given to Moses and Jesus and to the Prophets from their Lord; we make no distinction between any of them, and to Him (God) we submit."[Qur'an; 3:83]
Islam has three essential aspects or levels. They are Islam, Iman and Ihsan.
Islam, In the lexical context, means surrender and submission to the commands of Allah Ta'ala. This meaning occurs in the Qur'an:"Then, when (Ibrahim (alayhi-salam) and his son) had both submitted (to Allah's command for Ibrahim (alayhis-salam) to sacrifice his son), and (Ibrahim) laid (his son) down on his forehead."[surah as-Saffat; 37:103] Islam also shares the same root as "salam" which is peace, and thus it conveys the meaning of attainment of or bringing about of peace. A Muslim is a person who has entered into peace
Iman (belief) lexically means affirmation and confirmation in the heart.
Ihsan, means goodness, to strive for excellence in achieving piety. All these of these are explained in the infamous hadith found in the widely circulated and read Forty Hadith compiled by Imam Nawawi. It was narrated by 'Umar ibn al-Khattab (radiAllahi anhu), and is found in sahih Muslim;
"One day we were sitting in the company of the Messenger of Allah, peace and blessings be upon him, when there appeared before us a man dressed in pure white clothes, his hair extraordinarily black. There were no signs of travel on him. None of us recognized him. He sat with the Prophet, peace and blessings be upon him. Resting his knees against his and the palms of his hands on his thighs, he said, 'O Muhammad, tell me about Islam'.
The Messenger of Allah replied, 'Islam is to testify that there is no god but Allah and that Muhammad is the Messenger of Allah, to establish the prayer, pay the zakat, observe the fast of Ramadan, and perform the pilgrimage to the House if you are able to do so'. He said, 'You have spoken the truth,' and we were amazed at him asking and then verifying that he had spoken the truth. He then said, 'Inform me about Iman'.He replied, 'It is to believe in Allah, His angels, His books, His messengers, the Last Day, and in the divine destiny of both good and evil'. He said, 'You have spoken the truth'. He then said, 'Tell me about Ihsan'. He said, 'It is to worship Allah as if you see Him, for though you do not see Him, surely He sees you'. He then said, 'Inform me about the Hour'. He replied, 'The one who is asked knows no more than the one who is asking'. He said, 'Tell me some of its signs'. He said, 'That the slave-girl will give birth to her mistress, and barefoot, destitute shepherds will compete with one another in the building of magnificent buildings'.Then he (the questioner) went on his way but I stayed with him (the Prophet) for a long while. He said to me, 'Umar, do you know who this questioner was?' I replied, 'Allah and His Messenger know best'. He said, 'He was Gabriel. He came to instruct you in your religion."