You can peruse his website here. Scroll down to the Religious Movements section and click on Oneness Pentecostal. There many Trinitarians like Slick make attempts to understand and then counter Oneness theology, but actually just muddies the waters. I have not taken the time to respond to all of his articles, but I have read and wanted to reply to the two below. The first article will be in quotes. My response will follow in regular text.
Oneness and the word "person"
Oneness theology denies the Trinity doctrine and claims that there is one person in the Godhead who has manifested himself in three different forms: the Father, the Son, and the Holy Spirit. These "forms" are not three separate persons, but one person who occupied consecutive modes. The Trinity, on the other hand, is the teaching that there is one God who exists in three separate, simultaneous, persons. Please note, though, this is not saying there are three gods.
“Manifest” is actually how Paul described the Incarnation in 1 Timothy 3:16. Trinitarianism is a developmental dogma. It has taken hundreds of years to hammer out its foundations. That fact is demonstrated by the use of “separate…persons”. This term is often used in the book The Forgotten Trinity by Dr. James White. The term persons as used theologically by Trinitarians is problematic in itself not to mention confounding the notion further by separating them. Trinitarians such as White, Slick, or Edward Dalcour believe these separate persons have each their own mind, will and conscious. This is tritheism on its face. Also, I do not believe the early creeds spoke the persons of the Trinity as being separate rather they were distinct.
If there is no real difference in distinct and separate then why the fuss over Nestorius? There is a difference in distinction and separation. I beleive however that this nuance is the evolution of Trinitarianism. It is evolving further into its logical conclusion of tritheism. In fact William Penn spent about a year imprisoned in the Tower of London for recognizing this problem of "separate persons". To refute the notion He wrote a tract called “Sandy Foundations Shaken”. He wrote,
“If there be three distinct and separate persons, then three distinct and separate substances, because every person is inseparable from its own substance; and as there is no person that is not a substance in common acceptation among men, so do the scriptures plentifully agree herein; and since the Father is God, the son is God, and the spirit is God, (which their opinion necessitates them to confess) then unless the Father, son, and spirit, are three distinct nothings, they must be three distinct substances, and consequently three distinct gods.” (from Sandy Foundations Shaken)Contemporary Trinitarians acknowledge the problem of “persons”. Karl Rahner and Karl Barth are one of two trinitarian theologians that expressed issues with the the term. Other theologians such as Frank Stagg and John Miller were both Protestant scholars who rejected popular Trinitarianism also. Church historian Dr. Bruce Shelley in the book Church History in Plain Language writes:
“The word “person,” however, did not mean to the early Christians what it means today. To us, a person means someone like Tom, Dick, or Harry. But the Latin word persona originally meant a mask worn by an actor on the stage. In Trinitarian thought the “mask” is not worn by God to hide but to reveal his true character. It is clear that when we think of the Trinity, we should not try to think of three persons in our sense of the term, but three personal disclosures of God that correspond to what he is really like.”Shelley admits the problem but attempts to rationalize the apparent amputation of the word person from reality. A person is a self-conscious being. That is indeed why I am one person, and you, whoever might be reading, is indeed another separate person. I do have distinctions within my person, as does our Creator, however these distinctions are not separate to the point of being apart from me. Trinitarians see this problem and attempt to place a special theological meaning that can only refer to the Trinitarian explanation of persons. This is gracious, however it should be noted that it should be our goal as theologians to transfer our knowledge in a comprehensible and meaningful way. Clearly special meaning is the only way the Trinitarian notion stands erect.
If this point is dismissed by Trinitarians then let me ask further. Why do you assign the term "person" to God at all? Is it to establish a way for us to comprehend how God exists in human terms? It would seem then that the appeal to special meaning is in fact contradictory to the very reason for assigning such meaning in the first place.
I believe Oneness Theology does not have a problem with “personal disclosures” as Shelley states. It does not necessarily refer to three separate persons giving the disclosures. In Oneness theology God is aware of Himself as existing in two distinct modes. As God Himself and God existing as a man. Separate persons giving unique disclosures of their selves smacks of tritheism. This should logically mean then that three divine, eternal subsistence’s each have their own center of consciousness. This sounds like something closer to an early Greek mythological description than a Biblical one in my opinion. In fact, if we read early Trinitarian apologists like Justin we might realize how such philosophical meaning became infused with Christian theology in the first place. The Trinitarian notion of persons and pre-existence is not wholly outside Old Testament and New Testament theology.
In defending the doctrine of the Trinity and in examining the Oneness doctrine regarding the Godhead, it is first necessary to define the terms that are used. Since the Trinity doctrine states there are three persons in one Godhead, and Oneness Pentecostal theology states there is only one person, we first need to know what a "person" is before we try to discover whether or not God is three persons or one. Therefore, we need to ask what qualifies someone as having "personhood"?
I offer the following analysis as an attempt to adequately define personhood. After the outline, I will try and show that the definition and/or characteristics of personhood can be applied to both the Father and the Son in a context that shows they both existed as persons at the same time, thereby proving Oneness theology is incorrect.
What are the qualities and attributes of being a person?
1. A person exists and has identity.
2. A person is aware of his own existence and identity.
A. This precludes the condition of being unconscious.
A self aware person will use such a statement as "I am", "me", "mine", etc.
A person can recognize the existence of other persons.
. This is true provided there were other persons around him or her.
A. Such recognition would include the use of such statements as "you are", "you", "yours", etc.
A person possesses a will.
. A will is the capability of conscious choice, decision, intention, desire, and or purpose.
A single person cannot have two separate and distinct wills at the same time on the exact same subject.
. Regarding the exact same subject, a person can desire/will one thing at one moment and another at a different moment.
A. Separate and simultaneous wills imply separate and simultaneous persons.
A person has the ability to communicate -- under normal conditions.
Persons do not need to have bodies.
. God the Father possesses personhood without a body, as do the angels.
A. Biblically speaking, upon death we are "absent from the body and home with the Lord" (2 Cor. 5:8).
God qualifies as having personhood in that He exists, is self aware, has identity, uses terms such as "Me", "I AM", "My", and possesses a will.
The question now becomes whether or not there is more than one "person" in the Godhead.
"Let this cup pass from Me."Slick does make a good point. “My” (adjective) is properly serving to describe the relationship between the Father and the Son. Jesus is indeed the Son of God, and can rightly say that God is His Father. The only begotten. The Incarnate expression of God Himself. Deity united inseparably and permanently with humanity. The Father is God existing as God. Jesus is God existing as God and man united together inseparably.
"And he was withdrawn from them about a stone’s cast, and kneeled down, and prayed, 42Saying, 'Father, if thou be willing, remove this cup from me: nevertheless not my will, but thine, be done'" (Luke 22:42).
"And he went a little further, and fell on his face, and prayed, saying, 'O my Father, if it be possible, let this cup pass from me: nevertheless not as I will, but as thou wilt'" (Matt. 26:39).
In both Luke 22:42 and Matt. 26:39 (which are parallel passages), the context is Jesus in the Garden of Gethsemane, right before His betrayal. He was praying to the Father about the ordeal He was about to undergo. Several points are worth bringing out here.
First, in this passage, Jesus addresses the Father. He says, "Oh my Father..." Note that Jesus says "my" and "Father." These two words designate a "me and you" relationship.
The assumption though, which is not necessary to the text, is that the “me and you” is actually two persons. This has yet to be proven. A plural persons is not an adequate meaning to impose upon the God of the Hebrews (See Deuteronomy 6:4).
Second, "If it be possible" is Jesus expressing a desire, a hope. What is that hope or desire? It is that "this cup pass from me." The cup Jesus is speaking of is the immanent ordeal of betrayal, scourging, and crucifixion. Jesus did not want to go through this. He was expressing His desire. It was His will not to undergo the severe ordeal ahead of Him. If this was not so, He would not have expressed the desire to have the cup pass from Him.
Third, in Matt. 26:39, Jesus says, "Nevertheless., not my will, but thine, be done." In Luke 22:42 he says, "Nevertheless not as I will, but as thou wilt." With this, Jesus is expressing His will and contrasting it to the will of the Father. Yet, He is stating that even though He does not want to undergo what lay ahead, "Nevertheless," He would submit to the will of the Father -- and not his own will.
This shows that the person of Jesus had a separate and different will than the Father. Since we have two separate simultaneous wills, we have two separate and simultaneous persons and Oneness Pentecostal theology is incorrect.
2. "Sandy Foundation Shaken" by William Penn. Above text cited from here. Other Biographical info concerning Penn.
3. Church History in Plain Language, by Shelley, Bruce L. Updated 2nd ed. Dallas, Tex.: Word Pub., 1995.