Know, may Allah have mercy on you, that it is obligatory upon you to hake knowledge of four matters:
1. Knowledge of (al 'ilm), which is knowledge and awareness of Allah, and knowledge of His prophet, and knowledge of the religion of islam with the proofs.
2. Action upon that.
3. Calling to that.
4. Patiently perservering and bearing any harm encountered on the way.

The proof is the saying of Allah, the Most High: "By time, mankind is in loss, except for those who truley believe and worship Allaah alone, and do righteous deeds, performing that which is obligatory upon them and avoiding that which they are forbidden, and enjoin one another with obedience to Allaah, and enjoin one another with patient perserverance upon obedience to Allah and upon facing harm and trials." Sooratal-'Asr (103)
Ash Shaafi'ee may Allah , the most high, have mercy upon him said "if Allah had sent down to His creation no other proof besides this soorah, it would have been sufficient for them." Al-Bukhaaree, may Allah have mercy upon him said " chapter: knowledge preceeds speech and action."
And the proof is this saying of Allah the Most High: "Know tht none has the right to be worshipped except Allah, and ask forgiveness of your Lord for your sins." (soorah Muhammad (47):19)
So He began by mentioning Knowledge before speech or action