Why do Christians believe in three gods?

How can you quote from the Bible when it has been altered or corrupted?

How can Jesus be the Son of God?

Why are the manuscripts of the New Testament in Greek when Jesus spoke Aramaic?

Why do Christians believe in three gods?

It is true that the Qur'an says:

Allah is the third of three
(Surah 5:73)
And behold! Allah will say: "O Jesus the son of Mary! Didst thou say unto men, 'Worship me and my mother as gods in derogation of Allah?"
(Surah 5:116, tr. Yusaf Ali)

You may have been taught that this is because Christians worship three gods. However, Christians do NOT believe in three gods as the Bible says:

The Lord our God, the Lord is One.
(Deuteronomy 6:4)

It is recorded in the gospel of Mark that Jesus used this very verse himself when asked, "Of all the commandments, which is the most important?":

"The most important one," answered Jesus, "is this: 'Hear, O Israel, the Lord our God, the Lord is one. Love the Lord your God with all your heart and with all your soul and with all your mind and with all your strength.'"
(Mark 12:29,30)

Indeed, we believe in ONE God and love him with all our heart, soul, mind and strength.

How can you quote from the Bible when it has been altered or corrupted?

This presents the question, when was the Bible altered or corrupted? It could not have occurred after the time of Muhammad as there is much evidence that the Bible is materially the same now as it was then. If it was before the time of Muhammad, Muslims have problems with their own scriptures for the Qur'an says:

The Word of thy Lord doth find its fulfilment in truth and in justice: none can change His Words: for He is the one Who heareth and knoweth all.
(Surah 6:116)

For them are Glad Tidings, in the life of the Present and in the Hereafter: no change can there be in the Words of Allah. This is indeed the supreme Felicity.
(Surah 10:64)

A more detailed discussion can be found in the discussion topic, The Integrity of the Bibl.

How can Jesus be the Son of God?

Firstly, let's be clear about this, Christians do not use the title 'Son of God' to mean that God took Mary to be his wife. At the time of Muhammad it was widely believed that Allah had many sons and daughters. Muhammad, in rejecting this belief, thought that Christians had a similar belief. Christians and Muslims agree that Jesus was born of the virgin Mary, and that Jesus is the word of God and and a spirit from God. In the Bible we read:

The Word became flesh and made his dwelling among us. We have seen his glory, the glory of the One and Only, who came from the Father, full of grace and truth.
(John 1:14)

"How will this be," Mary asked the angel, "since I am a virgin?" The angel answered, "The Holy Spirit will come upon you, and the power of the Most High will overshadow you. So the holy one to be born will be called the Son of God.
(Luke 1:34,35)

Christians use the term 'Son of God' meaning that he is the eternal word of God as stated in the Qur'an (Surah 3:45), having been in existence from the beginning:

In the beginning was the Word, and the Word was with God, and the Word was God. He was with God in the beginning.
(John 1:1,2)

In calling Jesus the 'Son of God' we are merely stating our belief that Jesus is God's eternal Word, born of the Spirit of God to the Virgin Mary, to reveal God's likeness (John 14:9) and to save the world from the wages of sin (Romans 6:23 and John 3:17).

We believe that through Jesus, God who is Al-baten - the hidden, became Az-zaher - the revealed. No one has seen the Father (al-baten) but the son has revealed him (as being his az-zaher).

Why are the manuscripts of the New Testament in Greek when Jesus spoke Aramaic?

We don't know why God chose the Greek language for inspiration, but we should not lay restrictions on Him. However, it was the universal language of that time right up until1000 AD.

When we read the Qur'an, we find verses in Arabic which are said to be the words of Jesus (Surah 3:49-54; 5:114-118; 61:14 etc.). Indeed Muslims believe that they are words of Jesus. Now, if Jesus' words can be recorded as the word of God in Arabic, a translation, then surely his words can also be recorded in the Greek language of the Christian Scriptures.

One may also find words spoken by various prophets in the Qur'an. Most of these prophets spoke Hebrew but their words are also recorded in Arabic in the Qur'an. So one can see that Muslims don't have these people's original words either. In spite of this, if such a situation does not effect the integrity of the Qur'an, then nor should it be treated as evidence to question the integrity of the Bible.