Sooratul-’Asr 103:1-3 –
“If Allaah had not revealed any proof to His creation other than this soorah, it would have been sufficient for them.”
Indeed it is obligatory upon every Muslim to know four matters and to act upon them, and these matters are: [i] Knowledge; [ii] Acting upon it; [iii] Calling to it; [iv] Being patient with the hardship encountered due to it.
Indeed an incitation towards these four matters has occurred in Sooratul-’Asr:
“By the time, verily man is in a state of loss. Except those who believe and perform righteous deeds, and advise each other to the truth, and advise each other to patience.” [Sooratul-’Asr 103:1-3]
So indeed Allaah the Exalted swears by the time, and Allaah the Exalted can swear by anything from His creation, contrary to the creation itself. So it is not permissible for the creation to swear, except by Allaah the Exalted, or by an Attribute from His Attributes. And the answer of this swearing is that: “…verily man (al-Insaan) is in a state of loss.” And ‘al’ in al-Insaan means definitiveness. That is to say, all of mankind are losers, except those who can be described with these four characteristics. So these bring one out of the state of loss, and these four characteristics comprise al-eemaan (faith). So there is no doubt that this eemaan must be built upon knowledge. And this knowledge is the recognition of Allaah the Exalted by His Attributes, and the recognition of His Messenger (sallallaahu ’alayhi wa sallam), and the recognition of the Religion of Islaam by its proofs. So action must follow this knowledge by way of statement, deed, and belief. Allaah the Exalted said:
“So know that there is no deity worthy of worship besides Allaah, and repent for your sins.” [Soorah Muhammad 47:19]
Indeed Imaam al-Bukhaaree (d.256H) – rahimahullaah – inserted a chapter in his book to illustrate this, so he said:
“Chapter: Knowledge comes before statement and action.”  So Allaah pointed out the second matter by His statement: “…and do righteous deeds…” So knowledge without action is like a body without a soul. Therefore, there can be no benefit in it, rather it becomes an argument against its owner. Allaah the Exalted said:
“O you who believe! Why do you say that which you do not do? It is extremely hateful to Allaah that you say that which you do not do.” [Sooratus-Saff 61:2-3]
So the action cannot be righteous, except if it is done purely for Allaah, in accordance to the Sharee’ah of Allaah. Then Allaah pointed out the third matter by His statement: “…and advise each other to the truth…” This refers to da’wah (calling to Allaah) upon knowledge, wisdom and a good preaching, as Allaah the Exalted said:
“Say: This is my way, I call unto Allaah. I and those who follow me, and I am not from amongst the polytheists.” [Soorah Yoosuf 12:108]
Then He pointed out the third matter by His statement: “…and advise each other to patience.” Therefore, it is inevitable that the one who calls to Allaah must be patient and take into consideration that which he will encounter of hardship along the way of teaching and calling to Allaah. So he must follow the path of the Prophets and Messengers and become patient where they were patient, until the call to Allaah has been conveyed; despite whatever he encounters from hardship in that.
So therefore, this is the accurate depiction of an enormous illustration, clarifying that which it is obligatory for the Muslim to be upon from a knowledge-based practical application of Islaam in a way which will be pleasing to Allaah the Exalted. Imaam ash-Shaafi’ee (d.204H) – rahimahullaah – said: “If Allaah had not revealed any proof to His creation other than this soorah, it would have been sufficient for them.” 
[FOUR FUNDAMENTAL PRINCIPLE OF DA’WAH]
 The following is taken from Mukhkiratun fil-’Aqeedah (p. 57-58) of Shaykh Saalih as-Suhaymee.
 Refer to the Saheeh of al-Bukhaaree (1/159).
 Related by Ibn Katheer in his Tafseer (8/500)
Translated by Maaz Qureshi 
– Shaykh Saalih Ibn Sa’d as-Suhaymee, http://www.troid.ca