Imam Al-Hasan Al-Basri defined human being, saying, "O man, you are nothing but a number of days; whenever a day passes away, a part of you passes away as well". Thus, the passage of time consumes man as days go by. Since the human being is nothing but time, Allah the Almighty swears time in general.

He says:

"By Al-'Asr (the time).* Verily! Man is in loss"

[Al-Asr, 1-2]

The passage of time causes man's loss. In other words, the passage of time alone consumes man. Thus, as I have mentioned above, since man is nothing but time, Allah the Almighty swears by time. After that, Allah the Almighty mentions the second part of His oath, He says:

 "Verily! Man is in loss"

[Al-Asr, 2]

Whether one is a believer or not, the passage of time consumes him.

Dr. Umar AbdulKafi:

Some scholars said, "One of the signs of being disliked by Allah the Almighty is wasting one's time" i.e. when one wastes his time, he actually wastes his life, which is the most precious thing  Allah, the Lord of creation, has granted him.

Dr. Rateb Al-Nabulsi:

However, Allah the Almighty, in a great manifestation of His Mercy, made four exceptions to that rule; to man's loss, He says:

"Except those who believe (in Islamic Monotheism) and do righteous good deeds, and recommend one another to the truth (i.e. order one another to perform all kinds of good deeds (Al-Ma'ruf) which Allah has ordained, and abstain from all kinds of sins and evil deeds (Al-Munkar) which Allah has forbidden), and recommend one another to patience (for the sufferings, harms, and injuries which one may encounter in Allah's Cause during preaching His religion of Islamic Monotheism or Jihad, etc.)"

[Al-Asr, 3]

The following Du'a is mentioned in some traditions: 

"There is no blessing for me in a day when I do not enhance my knowledge, and there is no blessing for me in a day when I do not get closer to Allah."

Imam ash-Shafi'I said about Surat Al-Asr, "If people ponder deeply over this Surah, it will be sufficient for them.'' The four requirements to avoid loss as mentioned in this Surah are as follows: first, searching for the truth, making sure of it, and believing in it. Second, acting upon the truth and calling people to it (to call people to Allah). Third, advising each other to adhere to the truth. Finally, remaining patient while searching for the truth, acting upon it, and calling people to it.