Oh but I do! The OT righteous did not believe in Three Persons united in one Divine Essence (Nature) in a perfect loving community that we know as God(head). The post-Jamnia Judaism (derivative of Pharisees) doesn't either.
But your entire argument appears to be premised on judging OT Jews by today's standards. Certainly you cannot hold the OT righteous accountable for the "new" teachings of Jesus, for example. For the OT righteous, the circle was not yet complete. Jews of today, OTOH, have no such excuse. So I don't think it is fair to judge an OT Jew based on whether he had a fully developed idea of the Trinity.
The Jews know God through the Law; we know God through Christ. The most important difference is that Judaism does not believe man needs to be saved. We do.
Sure, the OT Jew knew what he knew based on what God gave him to know. If faith is a gift of God, then what is the evidence that God gave any of them "faith" in a form that is substandard? Were the OT righteous given a fully developed plan of salvation through Christ that they all rejected? Which of God's teachings that He gave to the OT righteous did they reject and so are not saved?
Your Calvinist friends believe some are acceptable [to God] because they were pre-destioned from all eternity to be acceptable.
Yes, my Calvinist friends do believe that. And SO DO my Catholic friends! :)
Messianic anticipation in Judaism did not begin until about a century before Jesus was born.
What? Do you mean that every Jew just ignored chapters of scripture such as Isaiah 53 (from about 700 B.C.)? How could any of the OT righteous have BEEN righteous if they didn't believe in their own scripture?
We should emphasize what you rightfully pointed out as true, the only reason any of us are acceptable to God is because God has made us that way. This is what grace is all about. And the Bible clearly states this was before the foundations of the world when our names were added to the Book of Life.