He claims that the Qur’aan is lacking in eloquence and contains grammatical errors
Question

                In Soorat al-Baqarah it says (interpretation of the meaning): 

“And indeed, We gave Moosa (Moses) the Book and followed him up with a succession of Messengers. And We gave ‘Eesa (Jesus), the son of Maryam (Mary), clear signs and supported him with Rooh-ul-Qudus [Jibreel (Gabriel)]. Is it that whenever there came to you a Messenger with what you yourselves desired not, you grew arrogant? Some you disbelieved and some you killed”

[al-Baqarah 2:87] 

My Christian colleague says, look at the way the word taqtuloon (translated as “you killed” – appears in present tense form) follows the word kadhdhabtum (“you disbelieved” – past tense). He says that the wording should be [Allaah forbid that we should alter His Holy Book] fa fareeqan kadhdhabtum wa fareeqan qataltum (Some you disbelieved and some you killed) [i.e., both verbs appearing in past tense form], because the Prophets have ceased and Muhammad was the Seal of the Prophets. It should be noted that he does not believe that the Prophet Muhammad was a Prophet, rather he believes that Prophet ‘Eesa (Jesus) was the last of the Messengers. 

In Soorat Aal ‘Imraan it says (interpretation of the meaning): 

“When He has decreed something, He says to it only: ‘Be!’__and it is [kun fa yakoon]”

[Aal ‘Imraan 3:47] 

My Christian colleague also thinks that this is ineloquent and he says that it would be more correct [Allaah forbid that we should alter His Holy Book] to say Kun fa kaana (Be and it was).  

Please explain so that I can refute his comments. “So ask the people of the Reminder if you do not know” [al-Anbiya 21:7 – interpretation of the meaning].
Praise be to Allah.Firstly: 
The one who is not able to engage in debate 
    with others should fear Allaah and not get involved in debates and arguments with others; rather he should try to protect his religious commitment 
    by refraining from arguing with the ignorant or those who promote specious arguments.  
Secondly: 
With regard to the specious arguments 
    mentioned – which are more flimsy than a spider’s web – these may be answered in two ways. 
The first way is in general terms, which is 
    to say that the Qur’aan is the Book of Allaah which was revealed to the pure Arabs, who were the most advanced nation in the field of eloquence; 
    they paid a great deal of attention to that and had reached a high level of eloquent self-expression. They had established festivals of poetry and 
    speech-giving, they hung their mu’allaqaat poems on the Ka’bah as a sign of the high esteem in which they held eloquence and literature; they 
    competed in poetry and beautiful speech. Poetry flowed through their veins and they recited poems on all occasions, for joy and sorrow, birth and 
    death, happiness and misery, victory and defeat. This was something that was unknown in any other nation. 
Hence by His wisdom Allaah revealed to them 
    this Qur’aan in this language of which they were so proud and because of which they thought themselves superior to other nations. The Qur’aan 
    dazzled them with its beautiful words and meanings, its great purpose and structure. So they submitted to it out of respect for its language and 
    dare not speak any word of criticism against its wording, grammar or expression.  
Allaah challenged them in His Book to produce 
    anything like the Qur’aan, but they could not match it, let alone find fault with its grammar. Allaah says (interpretation of the meaning): 
“Say: ‘If the mankind and the jinn were 
    together to produce the like of this Qur’aan, they could not produce the like thereof, even if they helped one another’”
    [al-Isra’ 17:88]
Then Allaah challenged them to produced ten 
    soorahs like it, as He said (interpretation of the meaning): 
“Or they say, ‘He (Prophet Muhammad) 
    forged it (the Qur’aan).’ Say: ‘Bring you then ten forged Soorah (chapters) like unto it, and call whomsoever you can, other than Allaah (to your 
    help), if you speak the truth!’”
[Hood 11:13]
When they were unable to do that, then Allaah 
    challenged them to produce just one soorah like it. Allaah said (interpretation of the meaning): 
“And if you (Arab pagans, Jews, and 
    Christians) are in doubt concerning that which We have sent down (i.e. the Qur’aan) to Our slave (Muhammad), then produce a Soorah (chapter) of 
    the like thereof and call your witnesses (supporters and helpers) besides Allaah, if you are truthful”
[al-Baqarah 2:23]
No one who comes afterwards, when the 
    language has become corrupted and mixed with foreign languages, has any right to support such nonsensical ideas that do no more than point to the 
    depth of his ignorance and the shallowness of his thinking, and his lack of knowledge of the Arabic language. As it was said,  
“How often do you see someone criticizing 
    something that is sound, and his problem is that he cannot understand it properly.” 
The second way is in specific, detailed 
    terms, discussing the aspects of eloquence in the words that he criticized. This is as follows: 
With regard to the words of Allaah 
    (interpretation of the meaning): 
“Some you disbelieved and some you killed 
    (fafareeqan kadhdhabtum wa fareeqan taqtuloon)”
[al-Baqarah 2:87]
The scholar al-Taahir ibn ‘Ashoor said in his 
    commentary (al-Tahreer wa’l-Tanweer, 1/598): 
The word taqtuloon (translated as “you 
    killed”) appears in the present tense form to emphasize more vividly the terrible action that they did, namely killing the Prophets. This is like 
    the verse in which Allaah says (interpretation of the meaning): 
“And it is Allaah Who sends [arsala – part 
    tense form] the winds, so that they raise up [fa tutheeru – present tense form] the clouds, and We drive them to a dead land, and revive therewith 
    the earth after its death”
[Faatir 35:9]
Moreover, the form taqtuloon fits with 
    the rhyme of the soorah and makes it more vivid; this provides eloquence of meaning and beauty of form. End of quote. 
Shaykh Ibn ‘Uthaymeen quoted in his 
    Tasfeer (1/283) from some of the scholars another reason for using the present tense form taqtuloon, which is to provide a sense of 
    continuity, i.e., the Jews kept on killing the Prophets, even the last of them, Muhammad  (peace and blessings of Allaah be upon him). They 
    killed the Prophet  (peace and blessings of Allaah be upon him) with the poison that they gave him at Khaybar, and he  (peace and 
    blessings of Allaah be upon him) continued to suffer the effects of that until, in his final illness, he said, “I still feel pain from the food I 
    ate at Khaybar. This is the time when it has cut off my aorta.” 
Abu Dawood; also narrated by al-Bukhaari in a 
    mu’allaq report. Al-Albaani said in Saheeh Abi Dawood (3784), it is hasan saheeh. 
With regard to the verse in which Allaah says 
     
(interpretation of the meaning):
“When 
    He has decreed something, He says to it only: ‘Be!’ __and 
    it is [kun fa yakoon]”
[Aal ‘Imraan 3:47]
This is more indicative of the ignorance of 
    this objector, because this verse is speaking of when Allaah wills to create something in the future, not in the past; this is to be understood 
    from the use of the word idha (meaning when, if), which refers to something in the future. Hence the verb yaqool (says) appears in 
    the present tense, to indicate that it is referring to something in the future, and it is followed by the verb yakoon (it is), also in the 
    present tense, which also refers to something in the future. 
And Allaah knows best.