Reflecting long enough to consider what it means to be the Founder of our faith, which is also called the Way of G-d, you will have your answer.
The word Founder in English comes from the verb found which according to the New Oxford American Dictionary means:
To establish or originate something especially by providing an endowment.
This same dictionary ...
I think a possible interpretation is that G-d used a malaach / appeared to Avraham through a malaach, and that's what Avraham saw. Perhaps one can understand the word malaach as more of an agent, than a messenger. And the bible often uses the language of agency in relation to malaachim.
e.g. the Lord will destroy sodom, and the Malaachim do.
And you can ...