“You will die and they will die, and Muhammad is but a Messenger; of a surety, all Messengers before him have passed away. If then, he die or be slain, will you turn back on your heels? Whosoever worships Muhammad (SAW), let him then know that Muhammad indeed is dead; but whoso worshipped Allah (SWT), let him know that Allah lives and does not die.”
After the death of the Prophet (PBUH), the Muslims wondered if it would be possible for the Islamic community to carry on the torch of Islam without the leadership and guidance of the Prophet (PBUH).
Therefore, after the departure of the Prophet (PBUH) from this world, Umar and Abu Bakr became the torch bearers of Islam and they helped people strengthen their belief in Allah. These were the people who finally laid the foundations of the Islamic empire.
Abu Bakr became the first caliph of Islam. He faced many problems during his leadership as war broke out between several tribes. The first caliph mostly focused on restoring peace and suppressing the wars and rebellions.
After the death of Abu Bakr, Umar became the second caliph of Islam. Umar was a strong leader in that he had both military and political capabilities. He created a political structure for the growing Islamic empire and followed the footsteps of the Prophet (PBUH) in being tolerant.
Both these caliphs strengthened the hold of Islam because they lived a Quran based life. If you will learn holy quran live life according to it, you will be able to encourage other non-believers to embrace Islam