I do not believe Jesus had a beginning, no matter how many Christians believe that.
Orthodox Christian belief does not believe that either.
Jesus Christ is not a created being.
However, His being proceeds from the essence of the Father.
Given that the Father is God and therefore eternal, it follows that Jesus Christ is likewise God and also eternal.
Jesus Christ is clearly a separate being from the Father, yet identical in essence.
The same could also be said of the Holy Spirit.
Thus the doctrine of the Trinity clearly identifies three beings in the Godhead yet identical in essence and unity of purpose.
Many find this kind of description difficult to follow and reject it because they cannot "understand" it.
However, this is worth pondering: If everything about God was fully understandable by man then either God is not God, or, man is God!
Neither of these two possibilities make any sense though...
The Bible tells us that full understanding will only occur once we are residents of Heaven.
There are a multitude of resources on the net and elsewhere for those who wish to delve into the actual Scriptural details that underpin this doctrine. (And I would encourage this since the descriptions given will undoubtably be better than my off-the-cuff characterisation given above.)
This purpose of this particular post is just to underline the fact that the doctrine of the Trinity is integral to what makes Christianity Christian. Those groups or individuals who abandon this doctrine invariably end up denying several of the other fundamental doctrines of Christianity and end up creating another religion, either corporately or individually, that is not Christian. The fact that they may read the Bible becomes irrelevant...