Christianity is plagued with trying to balance the Trinity with the monotheism of the Jews. There's little in the New Testament to clear things up, either. The JWs are not believers in the Trinity; rather, they believe that Jesus was, in premortality, Michael the Archangel, which is purely conjecture. But in Acts and other Christian writings, there seems to be a definite line drawn between Jesus and God. Check out the stoning of Stephen in Acts 7:
55 But he, being full of the Holy Ghost, looked up stedfastly into heaven, and saw the glory of God, and Jesus standing on the right hand of God,
56 And said, Behold, I see the heavens opened, and the Son of man standing on the right hand of God.
...
59 And they stoned Stephen, calling upon God, and saying, Lord Jesus, receive my spirit.
Any observer could deduce from just this one passage that Jesus and God were two different beings, which is how the JWs read it. So they say, well, if Jesus and God are two different beings, who's the next greatest being in Heaven? Michael the Archangel!
BTW, the above is only one example of differentiations between God and Jesus. Only in the writings of John is the relationship between the Father, Son and Man. JWs also don't believe that the Holy Spirit is an actual personage but, rather, the "active force" of God. In other words, when God commands, the active force is what carries out His will. JWs argue that they are the only Christians who believe in one God. They reason that if the Father is God, then Jesus can't be God, because God told Isaiah He is the only God, and there are no others. If there were others, He said, He would know about it. If I understand the Trinity correctly, the Father, Son and Holy Spirit are three manifestations of the same being, or entity.
JWs reject that out of hand.