The Bible makes it clear one cannot have another God and be safe.
There's no way to make the God of the Bible acceptable to a but a Trinitarian.
Even in the Old Testament it was Trinity.
New Catholic Encyclopedia, 1977 Edition, Vol. 13, p. 1021 -- The first use of the Latin word "trinitas" (trinity) with reference to God, is found in Tertulian's writings (about 213 A.D.) He was the first to use the term "persons" (plural) in a Trinitarian context.
Encyclopedia Americana, 1957 Edition, Vol. 27, p. 69 -- The word "Trinity" is not in Scripture. The term "persons" (plural) is not applied in Scripture to the Trinity.
World Book Encyclopedia, 1984 Edition, Vol. T, p. 363 -- Belief in Father, Son and Holy Ghost was first defined by the earliest general council of churches. This was the First Council of Nicaea in 325 A.D.
New International Encyclopedia, Vol. 22 p. 476 -- The Catholic faith is this; We worship one God in Trinity, but there is one Person of the Father, another of the Son and another of the Holy Ghost. The Glory equal -- the Majesty co-eternal. The doctrine is not found in its fully developed form in the Scriptures. Modern theology does not seek to find it in the Old Testament. At the time of the Reformation the Protestant Church took over the doctrine of the Trinity without serious examination.
Life Magazine, October 30, 1950, Vol. 29, No. 18, p. 51 -- The Catholics made this statement concerning their doctrine of the Trinity, to defend the dogma of the assumption of Mary, in an article written by Graham Greene: "Our opponents sometimes claim that no belief should be held dogmatically which is not explicitly stated in Scripture ... But the PROTESTANT CHURCHES have themselves accepted such dogmas as THE TRINITY, for which there is NO SUCH PRECISE AUTHORITY In the Gospels."