The Trinity in Genesis 1:1

[QUOTE=honeto]God as One is probably the oldest teachings dating back to the Old Testament times[/QUOTE]

The oldest teaching is that God is a singularity that is also a plurality. This is from the very first verse in the Bible:

 

בראשית ברא אלהים

 

In the beginning God created (Gensis 1:1)

 

אלהים Elohim (God) is a plural noun

 

ברא Bara (created) is a singular verb

 

ראשית (reshit) begininng is from ראש (rosh) meaning head, top, height, chief, best.

 

Thus the highest teaching about God is contained in the first three words of the Bible in which He presents Himself as a singularity that is also a plurality.