Itzhak Shapira is a Messianic Rabbi who runs Ahavat Ammi Ministries and is the author of the book "The Kosher Pig", a book panned by the Orthodox Community in Judaism.
Recently the Answering-Islam Facebook page had issued a warning that Shapira does not teach the Trinity, but an ancient heresy called Modalism.
Modalists deny the Trinity yet acknowledge Yeshua or Jesus as God. The problem is that the unity of the individual persons is taken to the extreme where Jesus is the same person as the Father or where they are merely different manifestations of God. On a side note although Oneness advocate Roger Perkins claimed he acknowledged that the Father and the Son as distinct persons, I am not sure what he means by that in light of his denial of the Trinity.
(However, I recently discovered that there are two types of Modalist, Synonymous and Successive. Successive means the Father, Son and Spirit exist at different points, whereas Synonymous means they exist at the same time but are not three distinct persons)
Back to Shapira, the "rabbi" had recently spent time in a video responding to Rabbi Yisroel Blumenthal on objections he raised with respect to the Trinity.
Although Shapira spends the majority of the video trying to demonstrate that YHWH or Ha Shem is a compound unity by quoting the Zohar, a Kabbalistic text, and quoting from the TANAKH.
However, 13 minutes roughly in the video (http://www.youtube.com/watch?v=Bu4EWiw9Os4), Shapira says the following:
"The Zohar explains that God is truly a compound unity, ok, and to argue that this is not is arguing against Judaism. That is why when a man approached Yeshua and asked him what is the greatest commandment, Yeshua replied in Mark 12:29 Shema Yisrael Adonai Eleheinu Adonai Echad. Christianity on the other hand misunderstood it's compound unity and understood that God the Father, God the Son and God the Holy Spirit are all three different personas, well that is not true either. That is not the point in my book and that's not what I believe. I believe that God is a compound God, he is ONE and he is absolute, without beginning and end, but at the same time he can manifest himself in anyway he chooses for".
And it is ALL downhill from here.
As I have said before, The Trinity teaches that in the very being or essence of God, there exist Three Distinct persons, Not three beings in one being or three persons in one person (like Ahmed Deedat falsely claimed). There are not three seperate Gods, but one Eternal God which the TANAKH and the NT make very clear. This is clearly something denied by Shapira.
I myself on a side note want to represent accurately what Rabbinic literature says properly. I have even occasionally spoken with orthodox Jews such as Funkdude and Sefard not Sefardi on some issues and ask for their perspectives and both have advised against using Shapira, which judging by what I have heard I am glad I didn't.
Yisroel Blumenthal has noted here the following:(http://yourphariseefriend.wordpress.com/2013/12/17/shapira-is-not-a-trinitarian/):
"Why did I assume that Shapira is a Trinitarian?
Simple; he claims to have been ordained by the IMACS which is a subsidiary of the MJAA. The statement of faith of the MJAA declares that the organization believes in the trinity. Furthermore; Shapira quotes extensively from Trinitarian books (such as “Can Three be One”) and from various Trinitarian Christians (such as Dr. Michael Brown). At no point does Shapira distance himself from the beliefs of those he quotes from."
Though I would disagree with Blumenthal that worship of Jesus is idolatry, that is not the topic of this article.
I find it a shame that Shapira is teaching the Modalist Heresy and I urge Shapira if he is reading what I write to abandon this heresy he is teaching, it is doing more harm to the Body of Christ than good.
Hope this article has been a help.
Addendum, Here is the video about this subject and Michael L Brown: http://www.youtube.com/watch?v=ynqRrHryPYo
Addendum 2: Shapira is not a Modalist in the sense of Successive Modalist, he is actually a Synonymous Modalist, For more details, read here: http://answering-judaism.blogspot.co.uk/2014/02/video-examination-of-itzhak-shapiras.html