If Allah is All-Knowing, why does He says this then?

(3: 166) and all that befell you on the day when the two hosts met in battle happened by God's leave, so that He might mark out the [true] believers, (3: 167) and mark out those who were tainted with hypocrisy and, when they were told, "Come, fight in God's cause" - or, "Defend yourselves"*** - answered, "If we but knew [that it would come to a] fight, we would indeed follow you." Unto apostasy were they nearer on that day than unto faith, uttering with their mouths something which was not in their hearts,**** the while God knew fully well what they were trying to conceal: (3: 168) they who, having themselves held back [from fighting, later] said of their [slain] brethren, "Had they but paid heed to us, they would not have been slain." Say: "Avert, then, death from yourselves, if what you say is true!"
*I.e., at the battle of Badr, in the year 2 H.

**Many of the followers of the Prophet had been convinced that, whatever the circumstances, God would grant them victory on account of their faith alone. The bitter experience at Uhud came as a shock to them; and so the Qur'an reminds them that this calamity was a consequence of their own doings.

***Only a fight in self-defence - in the widest meaning of this term - can be considered a "fight in God's cause" (see 2: 190-194, and the corresponding notes); and, thus, the particle "or" between these two phrases is almost synonymous with the expression "in other words".

****This is an allusion to the three hundred men who, on the way from Medina to Mount Uhud, forsook the Prophet on the specious plea that he did not really intend to give battle (see note 90 above). But since they knew in their hearts that it would come to a fight, their defection from God's cause almost amounted to a denial of Him (kufr, here rendered as "apostasy").


in simple terms that are lost to you in the translation. Allah swt wanted to make publicly known the believers from the hypocrites...

and Allah swt knows best

^good explanation,
God speaks in the present,past and future tenses, all being equal given that he is God.

also, there are the "seven letters" in which the qur'an was revealed, one of the letters is that all verb tenses are interchangeable, the past, present , future and order could substitute one another.
note in Arabic verbs also have an 'order' tense, so if one reads the letters comprising "Ya'llam" in this verse, it could be read as:

Ya'lam: he knows, present.

Yu'allim: he teaches, present.

Yu'lim: he informs, present,

and so on and so forth.

note there are two ways in which the "seven letters" are interpreted, one is that there are seven Arabic dialects that the qur'an could be read in, which is probably the most correct interpretation, the second one is very hard to explain to someone who is not a native speaker so 'll forgo it, note that I used the second one, which is still valid.

there is another construct called "the seven readings", these are different ways in which different mams of the past read the qur'an, the scholars have agreed that a "reading" is correct when:
it is possible to interpret the verses in that way, in either writing or meaning, ie. if the meaning is plausible in Arabic or if the meaning could be reached from the way the letters are arranged since in earlier Arabic script many vowels were not written,
and that the "sanad" or chain of narration stretching form the Prophet to the Imam reading in such a way is correct and sound.

for more, note that the link is in arabic

I discovered this hadith just yesterday and I love it.. wanted it for a siggy but it is too long..

while passing by the mosque I encountered people indulging in [insidious] talk. So I visited Ali 'and told him this. He asked me if this was true and I confirmed it. Then he said. I heard the prophet declare, '' dissension will certainly come''. I asked the prophet how it could be avoided, and he replied, ''kitabullah'': (the book of Allah) is the way; it contains information of what happened before you, News of what will come after you and a decision regarding matters that will occur among you. It is the distinguisher and it isn't jesting, if any overweening person abandons it, Allah will break him, and if anyone seeks guidance elsewhere Allah will lead him astray. It is Allah's stalwart rope, the wise reminder, the straight path; it is that by which desires don't swerve nor tongue becomes confused, and the learned cannot grasp it completely. It isn't worn out by repetition nor do its wonders every cease. It is that of which the Jinns didn't hesitate to remark when they heard it: we have heard a wonderful recitation which guides to what is right, and we believe in it'; he who utters it speaks the truth, he who acts according to is rewarded, he who pronounces judgement according to it is just, and he who invites people to it guides them to the straight path'' At-Tirmidhi, sunnan, hadith no.2906