It presents no problem at all. In fact, it fully supports trinitarianism. Be very careful in assuming that I haven't spent time thinking about it.1 Corinthians 8:6 presents a problem for the Trinitarian. I think you should spend some time thinking about what it says and what it means for the doctrine of the Trinity.
Deu 6:4 “Hear, O Israel: The LORD our God, the LORD is one. (ESV)
1Co 8:6 yet for us there is one God, the Father, from whom are all things and for whom we exist, and one Lord, Jesus Christ, through whom are all things and through whom we exist. (ESV)
Firstly, it really does look like Paul is expanding on the Shema to include both the Father and the Son in the one God and Lord. Secondly, if the Father and the Son are not distinct persons within the one God, then why even mention both here as distinct persons? Why does Paul and every other writer in the NT continually and consistently keep them distinct? If they are one and the same, this is not only pointless, it unnecessarily creates confusion.
If you believe that Jesus is Lord and that "this one Lord has to be the Father," then, by definition, you most certainly do not believe the Trinity.I have overcome this problem in my own thinking; I think that I believe in the Trinity even in light of the fact that there is one Lord Jesus Christ and that this one Lord has to be the Father according to Matthew 11:25, Luke 10:21, and 2 Corinthians 6:17-18.
Mat 11:25 At that time Jesus declared, “I thank you, Father, Lord of heaven and earth, that you have hidden these things from the wise and understanding and revealed them to little children; (ESV)
Luk 10:21 In that same hour he rejoiced in the Holy Spirit and said, “I thank you, Father, Lord of heaven and earth, that you have hidden these things from the wise and understanding and revealed them to little children; yes, Father, for such was your gracious will. (ESV)
Jesus is praying to the Father. Therefore, he cannot also be the Father.
I'm not sure what the passage from 2 Cor 6 has to do with anything.
As I have repeatedly stated in this thread, a son is never his own father nor a father his own son.
The Son has always existed, even as the Father has existed. That is what the doctrine of the Trinity states.The distinction being that the Father is a Spirit inhabiting eternity without flesh and the Son is the same Spirit inhabiting human flesh.