Almost one and a half years back When I stumbled in some Muslim forum I did not have any idea that Quran/Allah point out that we Christians are Polytheists and interpreted our belief in trinity as associating partners or other gods with God. They argue that we are worshipping three gods. Some said, "does God have three parts?" It was too annoying to hear that we Christians worship three gods. Later on I found out that in Quran, Allah has repeatedly said that associating partners with God is greatest sin as we read in:

An-Nisa (Women)

4:48 Allah forgiveth not that partners should be set up with Him; but He forgiveth anything else, to whom He pleaseth; to set up partners with Allah is to devise a sin Most heinous indeed.

Of course it is the greatest sin according to Bible also. When God gave Laws to Moses, the very first commandment He gave was, "You shall have no other gods before Me." (Exodus 20:3). Not only do we read in Old Testament but New Testament also asserts that there is only one God. Let us meditate on some of the verses from the Bible which says about ONE God. We read in Deuteronomy 6:4, "Hear, O Israel: The LORD our God, the LORD is one!

And in New Testament Jesus Himself quoted Deuteronomy 6:4 in Mark 12:29, "Jesus answered him, "The first of all the commandments is: 'Hear, O Israel, the LORD our God, the LORD is one."

Mark 12:32, So the scribe said to Him, "Well said, Teacher. You have spoken the truth, for there is one God, and there is no other but He."

While going further in New Testament we read the same ONE God in Paul's letters and other epistles as we read in Romans 3:30, "since there is one God who will justify the circumcised by faith and the uncircumcised through faith."

Ephesians 4:6, "one God and Father of all, who is above all, and through all, and in you all."

Let us look from the Bible 'what is trinity'. We read in Genesis 1:1-3 about all the three personalities of God. Gen 1:1-3, "In the beginning God created the heavens and the earth. The earth was without form, and void; and darkness was on the face of the deep. And the Spirit of God was hovering over the face of the waters. Then God said, "Let there be light"; and there was light." The above verses say about three personalities of God that is as follows:

1. God Himself
2. His Word (Jesus who is the very Word of God or Wisdom of God)
3. His Spirit (Holy Spirit)

And we read in Psalms 33:6, "By the word of the LORD the heavens were made, And all the host of them by the breath of His mouth." So again we see the three personalities of God in this verse, God, His Word and His breath (Holy Spirit).

Again we read in Proverbs 8:26-30, "While as yet He had not made the earth or the fields, Or the primeval dust of the world. When He prepared the heavens, I was there, When He drew a circle on the face of the deep, When He established the clouds above, When He strengthened the fountains of the deep, When He assigned to the sea its limit, So that the waters would not transgress His command, When He marked out the foundations of the earth, Then I was beside Him as a master craftsman; And I was daily His delight, Rejoicing always before Him."

So we can see that Wisdom of God or Word of God was with Him from the beginning who is none other than Jesus. And we also read about Holy Spirit who was also from the beginning. The same Word who was from the beginning came down as flesh in this world as we read in John 1:1-3 and John 1:14, "In the beginning was the Word, and the Word was with God, and the Word was God. He was in the beginning with God. All things were made through Him, and without Him nothing was made that was made." John 1:14, "And the Word became flesh and dwelt among us, and we beheld His glory, the glory as of the only begotten of the Father, full of grace and truth."

So Jesus and Holy Spirit are not partners of God but Jesus and Holy Spirit are the same Yahweh God. We are not associating other gods with Yahweh but it is the quality of Yahweh God. All three are inseparable though at the same time same ONE God. We can distinguish them as three different personalities but at the same time they are same ONE God. Let me give you one example. Take ONE coin. Coin has TWO sides. When you look from one side you will see a specific imprint but as soon as you turn it to the other side you can see a totally different appearance of this coin. Why? Can you say that there are two coins? No, there is only ONE coin but has TWO sides and both are different. We can distinguish both sides differently but we can not say that both sides are making two different coins. In the same way when we talk about Trinity, we can see three different personalities and three functions of God but at the same time there is only ONE God.

Many times Muslims say that there is no word "Trinity" in the Bible and if you want to see the history of Trinity you must go to the Nicene Creed which was written on 381 AD. So many think that Trinity or God the Father, God the Son and God the Holy Spirit came into existance only on 381 AD. But no, it is not true. If you want to see the history of Trinity you must go to the very first verse of the very first chapter of the very first book of the Bible where we see all the personalities of God. So trinity is from the beginning, it was not a brain-storm of Nicene Council.

Some say, "how it is possible that God the Father and God the Son can be one?" Let us read from Old Testament Isaiah 9:6, "For unto us a Child is born, Unto us a Son is given; And the government will be upon His shoulder. And His name will be called Wonderful, Counselor, Mighty God, Everlasting Father, Prince of Peace."

In this verse we read that, "Unto us a Son is given" and His name will be called "Everlasting Father". Again we see that God the Father and God the Son both are same ONE God.