Your identification is with the Father and with the Son. It cannot be with One and not the Other. If you are part of One you must be part of the Other, because They are One. The Holy Trinity is holy because It is One. (T-8.IV.8)
Some students, especially those that do not come from a Christian background, are confused by the dividing up of God into three parts -- Father, Son and Holy Spirit – in A Course in Miracles. Why not just say God?
The Course uses the Trinity of God just as it uses Knowledge and perception -- to distinguish the levels of the mind (see http://acimmentor.blogspot.com/2007/08/essential-distinction-knowledge-vs.html). Without the perception of separation from God it would not be necessary to speak of God in three parts. In God there is only God, Whole and Complete, not in parts but One. But in the perception of separation from God this awareness of Oneness is lost in a mind that thinks it is split between God and not-God (ego). The part of the mind that is still aware it is Part of God is called Christ/Son. Christ is the highest level of awareness you can reach in the world but it is still not yet the Oneness of God, Which is beyond the level of perception. The Holy Spirit is the teaching part of your Christ Mind. It is referred to as the Voice for God, Teacher, Comforter, Healer, Guide or Bridge because It is aware that you are Part of God but it is also aware you think you are something else (ego). The Holy Spirit teaches you to detach from ego and to identify with Christ instead.
You can call Christ or the Holy Spirit God because they are Part of God. But the distinction between the levels of the mind is important because confusing them is how the illusion of separation from God is maintained. This confusion makes it seem as though perception is reality. God (Father) is the Whole of Which Christ (Son) is a Part but becoming aware you are Part of God (Christ consciousness) is only preparation for accepting Reality -- God. Eventually you will let go of the perception level of the mind, though purified, in order to be lifted back to the Knowledge of God.
It cannot be emphasized too often that correcting perception is merely a temporary expedient. It is necessary only because misperception is a block to knowledge, while accurate perception is a steppingstone towards it. The whole value of right perception lies in the inevitable realization that all perception is unnecessary. (T-4.II.11)
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