Aplogies - this is fairly long.
(Old Testament | Isaiah 43:8 - 13)
8 ΒΆ Bring forth the blind people that have eyes, and the deaf that have ears.
9 Let all the nations be gathered together, and let the people be assembled: who among them can declare this, and shew us former things? let them bring forth their witnesses, that they may be justified: or let them hear, and say, It is truth.
10 Ye are my witnesses, saith the LORD, and my servant whom I have chosen: that ye may know and believe me, and understand that I am he: before me there was no God formed, neither shall there be after me.
11 I, even I, am the LORD; and beside me there is no saviour.
12 I have declared, and have saved, and I have shewed, when there was no strange god among you: therefore ye are my witnesses, saith the LORD, that I am God.
13 Yea, before the day was I am he; and there is none that can deliver out of my hand: I will work, and who shall let it?
Isn't the key to this that Jesus is speaking and verse 11 identifies the context? - Israel would be given no other God - there was no other God to whom Israel looked nor would there be one thereafter as only one God (using the title), Jesus, would be the Saviour for Israel. God the Father cannot save Israel nor can God the Spirit since we are being saved from hell which is the punishment of God the Father for disobedience (not a punishment from Jesus or the Spirit.) So we have one God (the Father) who offers choice to mankind (which entails the possibility of punishment as well as reward), we have one God (Jesus) who acts in the sacrificial role to 'atone' for bad choices and heal the rift and we have one God (the Comforter or Holy Spirit) who testifies of truth and communicates to our Spiritual side (should we listen.)
Together they are a trinity , a council a 'oneness' of purpose and aim all working on their part of the gospel plan. Israel, the family, the nation would have the singular honour and awful destiny to raise the only Begotten God (Jesus) as the sacrificial lamb and to act in the role of Priests to sacrifice Him. Their punishment has been severe and they have paid an unimaginable price for this and in their own way are saviours on Mount Zion (Jesus had to die and we must be glad our forefathers were not required to do this). The old testament ties Jesus closer to Israel and Israel closer to Him than we, as gentiles have any claim ((New Testament | Matthew 15:24) 24 But he answered and said, I am not sent but unto the lost sheep of the house of Israel. - (New Testament | Matthew 23:37) 37 O Jerusalem, Jerusalem, thou that killest the prophets, and stonest them which are sent unto thee, how often would I have gathered thy children together, even as a hen gathereth her chickens under her wings, and ye would not!)
(Old Testament | Deuteronomy 6:4)
4 Hear, O Israel: The LORD our God is one LORD:
This backs up the idea that Jesus is NOT the trinity - he is not three Gods in one - he is one Lord not many Lords....
(Old Testament | Isaiah 44:6 - 8)
6 Thus saith the LORD the King of Israel, and his redeemer the LORD of hosts; I am the first, and I am the last; and beside me there is no God.
7 And who, as I, shall call, and shall declare it, and set it in order for me, since I appointed the ancient people? and the things that are coming, and shall come, let them shew unto them.
8 Fear ye not, neither be afraid: have not I told thee from that time, and have declared it? ye are even my witnesses. Is there a God beside me? yea, there is no God; I know not any.
Jesus wasn't on the right hand of God at this point (nor was anyone else yet resurrected to godhood - oops LDS theology) - so in context I see no great problem with the above statement - in most cultures having someone beside you means you are equal and Jesus was not yet equal to His Father (LDS theology says this is becasue He needed a perfected resurrected body which Jesus did not yet have but does now.) Also no-one else was yet equal to Jesus (and no I'm not saying anyone else is yet.)
(New Testament | 1 Timothy 2:5)
5 For there is one God, and one mediator between God and men, the man Christ Jesus;
Err this looks very like an argument against the trinity by my reading but it perfectly agrees with my interpretation of Isaiah 43:8 - 13. If we use 'God' as a title/role then Jesus played many roles throughout His earthly life and while on the earth He was not playing the role of God per se but the role of Messiah. As He said to Mary in the garden - touch me not I have not yet ascended to my Father. When Jesus comes to the world again it will be as King and God. God is a title not an absolute solo individual but this is perhaps the most difficult concept we have when dealing with the conceptualisation of God - non of us agree what it means.