Why did the Prophet (peace and blessings of Allaah be upon him) not tell us when the Hour would begin?

Firstly: 

The Prophet (peace
and blessings of Allaah be upon him) did not tell us when the Hour would
begin because he did not know when the Hour would begin. We have already
quoted in question no.
32627 the evidence from the Qur’aan and Sunnah
concerning that. 

Secondly: 

If it is asked: why did Allaah not tell us when the Hour
would begin? 

The answer is that wisdom dictates that the time should be
hidden from mankind. 

The reason for that is that the Prophet (peace and
blessings of Allaah be upon him) was sent with glad tidings of Paradise for
those who obey Allaah, and with warnings of Hell for those who disobey Him,
and with warnings of the Hour and of Hell and its horrors. The purpose of
that can only be achieved if the time of the Hour is concealed, so that the
people of every era will fear that it may come upon them. Announcing the
time when it will happen would cancel out that benefit and would also have
other evil consequences. If the Messenger of Allaah (peace and
blessings of Allaah be upon him) had told the people: The Hour will come one
thousand years from today, for example, you would have seen the liars
mocking this idea and persisting in their disbelief, and the doubts of the
doubters would have increased. 

So there is great wisdom in concealing the matter of the
Hour, as Allaah has also concealed the time of each person’s own “Hour,”
meaning his death. 

Al-Aloosi (may Allaah have mercy on him) said: 

Allaah has concealed the knowledge of the Hour because shar’i
wisdom and reason dictate that this should be so, because that is more
effective in calling people to obey Him and putting them off disobeying Him.
Similarly he has also concealed the lifespan of each person. The verses
indicate that the Prophet (peace and blessings of Allaah be upon him)
did not know when the Hour would begin. Yes, he knew that it was close in
general terms, and he (peace and blessings of Allaah be upon him) told
us of that. 

End quote. 

So the believers must fear that Day and their fear should
make them aware that Allaah is always watching what they do. So they should
adhere to what is true and seek what is good, and they should fear evil and
sin, and they should not make the Hour the focus only of disputes and
arguments. 

End quote, from Tafseer al-Manaar. 

It is by Allaah’s mercy towards His creation that He has told
them of signs which will indicate that the onset of the Hour is approaching,
so that that will motivate them to do righteous deeds and fear Allaah, and
avoid haraam things. Every time they see one of its signs, their fear of the
Hour and its horrors will increase, as will their certainty that it is at
hand, so they will prepare for it by doing more righteous deeds. 

Allaah says (interpretation of the meaning): 

“Do they then await (anything) other than the Hour that it
should come upon them suddenly? But some of its portents (indications and
signs) have already come”

[Muhammad 47:18]

This is also indicated by the report narrated by Muslim
(2947), that the Prophet (peace and blessings of Allaah be upon him)
said: “Hasten to do good deeds before six things come to pass: the rising of
the sun from the west, the smoke, the Dajjaal, the Beast, and that which
will come to each one of you alone, and that which will affect everyone.”

Narrated by Muslim, 2947. 

This means: try to beat the six signs that the Hour has
begun, and hasten to do righteous deeds before they come to pass, for good
deeds done after they appear will not be accepted and will not count. 

“That which will come to each one of you alone” refers to
death. “That which will affect everyone” means the Resurrection. 

Al-Qaadi said: He commanded them to hasten to do righteous
deeds before these signs came to pass, for when they come they will dazzle
people and will distract them from doing anything, or will close the door of
repentance and acceptance of deeds to them. 

Al-‘Alaa’i said: The purpose of these reports is to encourage
us to start doing righteous deeds before we die, and to make the most of our
time before disaster comes. 

We ask Allaah to help us to make the most of our time in obeying Him. 

And Allaah knows best.