So, "one god" or "monotheism" isn't a quantity, but a quality. The "only one god" isn't talking about one being, but multiple beings that are [like a marriage] "one".
Maybe I simplified too much? "Multiple beings?" In as much as my thoughts are part of me - my "logos". Okay, let me try another tact. When a parent wants to speak about sexual matters to their child, it is done in an age appropriate manner. No parent is going to expect a child to have adult comprehension.
We are told the plan of God in a way that we, while in flesh, are able to understand in an age appropriate manner. Nature itself proclaims the "mystery". When we look a parables we are able to see without really seeing, that's the purpose. A farmer plants a seed, God speaks his word, the seed grows, Jesus interprets, roots are formed, we act on the truth, the plant grows, it is watered, kindness is shown by others. Can you look at a small seed and get a guess at what it will become? Can we know what a tree is while yet in germ form?
Well, as we go to another analogy the mystery is broadened. We know in marriage our body no longer belongs to us but to our spouse. We are the body of Christ. As we realize and act on this there comes to us the bread of life - the word of God - we pray and communicate with the Lord, walking with Him is our very air. The various parts of the body are alluded to in the bible - a foot should not be jealous to be an eye. Rather we are to understand that we are one body and together we walk with our betrothed, the "head" our king.
The blood brings both life and also removes impurities. When we see our brother sinning (not a sin that leads to death, there is a sin that leads to death, and I don't say pray for this) we are to pray and God will give LIFE. We know that all our prayers are answered because we pray according to the will of the Father. What is the will of the Father? It was demonstrated by the life of Jesus - he wants us to love the truth, to love justice AND mercy and to walk with Him.