Excellent points have been put forwarded to tell why Christians do not accept Muhammad as the prophet of God in the above answers given so far. Here I am adding few more to the above list of the reasons.
Since Muslims claim that Muhammad is the "last and the greatest" prophets of all it is but natural that we expect the best teachings that the world has ever seen and the highest moral standards of a living human being from Muhammad. Honest examinations reveals that Muhammad lacks both!
Jesus not only claimed authenticity from the previous Jewish books but also showed which scriptures actually foretold about him.
16 And He came to Nazareth, where He had been brought up; and as was
His custom, He entered the synagogue on the Sabbath, and stood up to
read. 17 And the scroll of Isaiah the prophet was handed to Him. And
He unrolled the scroll and found the place where it was written:
18 “The Spirit of the Lord is upon Me, Because He anointed Me to bring
good news to the poor. He has sent Me to proclaim release to captives,
And recovery of sight to the blind, To set free those who are
oppressed, 19 To proclaim the favorable year of the Lord.” 20 And He
rolled up the scroll, gave it back to the attendant, and sat down; and
the eyes of all the people in the synagogue were intently directed at
Him. 21 Now He began to say to them, “Today this Scripture has been
fulfilled in your [e]hearing.” (Luke.4:16-21)
This type of clear-cut Scriptural quoting is missing from Muhammad's claims.
Although he repeatedly claims that the Quran is given to confirm, not to correct or restore as some might wrongly assume, the previous Scriptures i.e. Torah, Psalms, prophets, and the Gospels, a close examination reveals his teachings are diametrically opposite to the previous Scriptures.
There were both Jews and Christians who had the previous Scriptures in their possession in the the same place where Muhammad lived and ruled. In fact, traditions [hadeeth literature] gave clear testimony that Muhammad did come in contact with the previous books, yet he never pointed to any particular parts in the previous scriptures [the Bible] in support of his so-called 'prophethood.'
Previous books talk about divorce, reason, and remarriage...
“When a man takes a wife and marries her, and it happens, if she finds
no favor in his eyes because he has found some indecency in her, that
he writes her a certificate of divorce, puts it in her hand, and
[a]sends her away from his house, 2 and she leaves his house and goes
and becomes another man’s wife, 3 and the latter husband [b]turns
against her, writes her a certificate of divorce and puts it in her
hand, and [c]sends her away from his house, or if the latter husband
who took her to be his wife dies, 4 then her former husband who
[d]sent her away is not allowed to take her again to be his wife,
after [e]she has been defiled; for that is an abomination before the
Lord, and you shall not bring sin on the land which the Lord your God
is giving you as an inheritance." (Deuteronomy.24:1-4)
"God [a]says, “If a husband divorces his wife And she leaves him And
becomes another man’s wife, Will he return to her again? Would that
land not be completely defiled? But you are a prostitute with many
[b]lovers; Yet you turn to Me,” declares the Lord." (Jeremiah.3:1)
Muhammad gave a book that goes diametrically opposite to the above Scriptural teachings...
“So if he divorces her she shall not be lawful to him afterwards until she marries another husband; then if he divorces her there is no blame on them both if they return to each other (by marriage), if they think that they can keep within the limits of Allah, and these are the limits of Allah which He makes clear for a people who knowe.”(Quran-Surah 2:230)
Previous books lay out clear punishment for the murder...
"30 ‘If anyone kills a person, the murderer shall be put to death on
the [o]testimony of witnesses, but no person shall be put to death on
the testimony of only one witness. 31 Moreover, you shall not accept a
ransom for the life of a murderer who is [p]condemned to death, but he
must be put to death." (Numbers.35:30-31)
But the book that Muhammad gave teaches the opposite and outrageous...
"O ye who believe! the law of equality is prescribed to you in cases
of murder: the free for the free, the slave for the slave, the woman
for the woman. But if any remission is made by the brother of the
slain, then grant any reasonable demand, and compensate him with
handsome gratitude, this is a concession and a Mercy from your Lord.
After this whoever exceeds the limits shall be in grave penalty."
True prophets referred to the Creator as the Father...
"Is this what you do to the Lord, You foolish and unwise people? Is He
not your Father who has purchased you? He has made you and established
"He will call to Me, ‘You are my Father, My God, and the rock of my
"“Pray, then, in this way: ‘Our Father, who is in heaven, [d]Hallowed
be Your name." (Matthew.6:9)
" I will declare the decree: the Lord hath said unto me, Thou art my Son; this day have I begotten thee." (Psalm.2:7)
But Muhammad's books teaches otherwise...
"He begets not, nor was He begotten." (Quran-Surah.112:3)
Prophets of the previous books never told that the eternal life will consist of pleasures related to the biological needs such as marriage. On the contrary they proclaimed that the redeemed/believers will not marry in world to come...
"29 But Jesus answered and said to them, “You are mistaken, since you
do not [s]understand the Scriptures nor the power of God. 30 For in
the resurrection they neither marry nor are given in marriage, but are
like angels in heaven." (Matthews.22:29-30)
Whereas Muhammad taught in his book...
"“Indeed, the people of Paradise will be happily occupied. They and
their wives shall be in shades, reclining on raised couches. There are
for them fruits and there is for them all that they ask
for...”(Quran-Surah 36: 55-57)"
"so it will be. We shall wed them to maidens with large, dark eyes"