One of the key points to God in Judaism is the following verse:
“Hear, O Israel: The LORD our God, the LORD is one. (Deu 6:4)
This verse seems to stand in the face of Christianity and declares the idea of the trinity as false teaching, as God is one.
“One” is an interesting word. The Hebrew word is ‘echâd or ‘echad. The word simply means one. This word, which means one, is found 952 times in the Old Testament.
In Genesis 1:5, one is used to signify the first day. Genesis 1:9, the waters are gathered together into one place. Genesis 2:11, it is used to signify that Pishon is the first of the three rivers. With Genesis 2:24, man and female shall come together in marriage and become one flesh.
I can see why some would reject the trinity as three is not one. As God said that man and woman would come together and be one flesh, we know that they do not become a literal one being, but rather the two should work together in union and harmony and present themselves as one force. So why can this not be the same with God?