Knowledge (arabic 'ilm, عِلْم) in Islam means knowing the truth with evidence. Knowledge leads to faith (Iman) and righteous actions. Without knowledge we cannot believe, we cannot do proper worship (praying, fasting, Hajj etc.) and we cannot distinguish between truth and falsehood. The most important knowledge is:

It is the highest form of knowledge. Allah is the creator, the provider and the sustainer of all things, the one who controls all affairs and everything shows the greatness of Allah. We know Allah through his revelation, his names, his attributes and trough his signs. There is no other deity except Allah. Allah created us, provided for us, sustains us and he did not leave us neglected, but rather he sent us a messenger. Whatever blessing we have is from Allah. Allah sent prophets to to guide mankind.

The name of the prophet ﷺ is Muhammad ibn Abdullah, he was born in Makkah and he is the final messenger. He taught humanity Tauhid, prayer, good manners, justice and mercy. Our duties to him ﷺ are that we believe him, obey him and that we follow his Sunnah. Whoever obeys him will enter paradise and whoever disobeys him will enter hell.

We have to know Islam with evidence from the Qur'an and the Sunnah. Islam means submission to Allah through Tauhid. Tauhid means that we worship only Allah and don't assign partners to him. Allah created us only to worship him alone, to obey him and to prepare for the hereafter. This is the purpose of life. A muslim submits himself to Allah by three things, namely obeying Allah, worshipping Allah and following his commands.