The orthodox Christian doctrine of the Trinity is impossible to fully understand. This should not surprise us because if we could comprehend the doctrine we would understand God, who is in-comprehensive. We would then be equal with God which is impossible.
However difficult it is to understand we need to believe it because it has been revealed to us in the Scriptures.
The Jehovah Witnesses and some other ‘Christian’ cults do not accept the doctrine of the Trinity. And as a result, they deny the deity of Christ. By denying the deity of the Son of God, they dishonour the Father as Jesus stated in John 5:23 “That all men should honour the Son, even as they honour the Father. He that honoureth not the Son honoureth not the Father which hath sent him.”
The argument below can be used to expose their old heresy.
W G T Shedd wrote in Dogmatic Theology p288, “The first person is not the eternal Father, before the second person is the eternal son. An eternal Father cannot exist before an eternal Son; if so, there would be a time when he is not the eternal Father. A Divine person who has no son is not a father.”
To put it simply the eternal Father cannot be childless at one point and then become a Father. To be the eternal Father he must have a Son from all eternity.