Unity' means 'not-unity'. There is only One God, the scripture is clear on this point. We, the believers, worship the One and only God. Idolatry is when more than one 'God' is worshipped. When the part is separated from the whole, the part becomes the 'whole'.
Idolatry is when the 'whole' is worshipped.
Natural man worships the 'whole', the 'God' of this world. The idea of the Father, the Son, and the Holy Ghost, refer to the Whole, the Part, and the Idea that the Part cannot be separated from the Whole. A believer's sins can therefore be forgiven because he believes that the Part cannot be separated from the Whole. A non-believer on the other hand, commits the unpardonable sin, because he believes that the Part can be separated from the Whole. A non-believer can only be forgiven when he confesses that he is a sinner, he cannot be forgiven for committing a 'sin', he is constantly sinning against the Holy Ghost.