Why do Christians have different beliefs that we have all the same God? No that is not true.
It is not true that we have the same God has Christians, we just call ourselves Christians sometimes, there are Christians calling themselves Christians but they are not suppose they agree that there is a discipline of God someone who obeys the law of christ wholeheartedly and completely, disobeying one of the law of christ will not merit you to be called a Christian or put aside or set aside one of the law of christ, you cannot be called a Christian, A real Christian is somebody who obey all the law of christ.
Matthew 28 verse 19 and 20 says, Go ye therefore, and teach all nations,baptizing them in the time of the father,and of the son,and of the Holy Ghost. Verse 29 says, teaching them to observe all things whatsoever I have commanded you, and, lo, I am with you always, even unto the end of the world.Amen. if you have noticed the word used by the lord jesus christ, "teaching them to observe all things".... all things not wanting, not lacking, not with addition. True disciplines or Christian are taught exactly what to do, no more, no less, all the commandments of christ.
One of the commandments of christ is to refuse or to refrain from idolatry. The question is why do Christians have different beliefs when we have same God? No its not true. No all so called Christians have the same God. Why? Galatians 1 verse 8, howbeit then, when ye knew not God,ye did serving unto them,which by nature are not Gods. There are groups of people serving God's which they believe,but by nature, their God's and no God's.