which is the most currect guide to mankind?

(2:185)
"Ramadan is the (month) in which was sent down the Qur’an, as a guide to mankind, also clear
(Signs) for guidance and judgement (between right and wrong)."

For what we are repent to allah earliar,we can repent when death approaches ?

(4:17)
'But of no avail is repentance of those who do evil until death approaches
any one of them and then he says: 'Now I repent.' Nor is the repentance 
of those who die in the state of unbelief of any avail to them. For them 
We have kept in readiness a painful chastisement.'

Is Allah is the very Truth?

(31:30)
'This is because Allah is the very Truth, and all 
those whom the people invoke instead of Allah, are 
false, and (this is because) Allah alone is the 
High, the Great.'  

who causes the night to pass into the day and the day into the night?

(31:29)
'Do you not see that Allah causes the night to pass into the day and 
the day into the night? He has subjected the sun and the moon, each 
voyaging (in its course) till an appointed time. And (do you not know) 
that Allah is aware of whatever you do?' 

Is'nt Allah knows every thing that happening in the world ?

(6:59)
'He has the keys to the realm that lies beyond the reach of
human perception; none knows them but He. And He knows what 
is on the land and in the sea; there is not a leaf, which 
falls that He does not know about and there is not a grain 
in the darkness of the earth or anything green or dry, 
which has not been recorded in a Clear Book.  He recalls 
your souls by night, and knows what you do by day; and then
He raises you back each day in order that the term appointed
by Him is fulfilled. Then to Him you will return whereupon 
He will let you know what you have been doing. And He alone 
holds sway over His servants and sets guardians over you till
death approaches any of you and Our deputed angels take his 
soul, neglecting no part of their task. Then all are restored
to Allah, their true protector. Behold, His is the judgment
.He is the swiftest of those who take account.'

Is allah have excellent names?

(59:23-24)
He is Allah besides Whom there is no god.
He is the Knower of the unseen and the seen:
He is the Compassionate and the Merciful.
He is Allah, besides Whom there is no god:
He is the Sovereign, the Holy, the Source
of safety, the Giver of peace, the Guardian,
the All-Mighty, the Enforcer of His decrees,
and the ever Supreme. Exalted is Allah alone
Who is the Planner of Creation, its Enforcer
and its Fashioner. His are the excellent
names. Whatever is there in the heavens and
the earth glorifies Him. And He is the All-Mighty
and the All-Wise.

we can call Allah in diffrent names?

(17:110)
"Say: ‘Call upon Allah, or call upon Rahman: by whatever name ye call upon Him,
(it is well): for to Him belong the Most Beautiful Names.‘"

You can call Allah by any name, but it should be a beautiful name,should not conjure up a
mental picture, and should have qualities that only Allah possesses.