There is a book of questions and answers by Pope John Paul II title Crossing the Threshold of Hope. One of the questions had to do with disbelief (in general) as I recall. Why do so many people reject the gospel news of Jesus Christ?
But, his answer was, some people reject God because they reject, for one reason or another, the way he has revealed hiimself.
Akin's answer was long, and I was getting lost in it. I like to get a little closer to the Bible itself where all the action is.
Aside from anything else, God is revealing himself and teaching us how serious sin is, what an offense it is, how people living immorally, especially worshipping false gods, are going to be judged.
There are other principles that come out of the study of the Old Testament. Judaism (at least as described in the Bible) is not a "deist" religion, where God created the world and then dropped all involvement in it.
On the general subject of the relevance of the Old Testament, the Church has much to say.
In the early church, Marcion was a heretic who rejected the entire Old Testament, because HE didn't like the image of God that comes out of it. Neither Jews, nor Christians (including Catholics) agree with Marcion.
One document that uphold the importance of the old testament is here,
entitled THE JEWISH PEOPLE AND THEIR SACRED SCRIPTURES
IN THE CHRISTIAN BIBLE issued by the Pontifical Biblical Commission
Now, another place where the importance of the Old Testament is brought out is in the Catechism of the Catholic Church. In this excerpt, the statement is basically emphasizing the importance of revelation in Genesis:
from paragraph 389:
389 The doctrine of original sin is, so to speak, the "reverse side" of the Good News that Jesus is the Savior of all men, that all need salvation and that salvation is offered to all through Christ. The Church, which has the mind of Christ, knows very well that we cannot tamper with the revelation of original sin without undermining the mystery of Christ.
There was a priest on EWTN cable tv who used to say, a thousand difficulties do not add up to one doubt.
editorial opinion: keep studying and don't get overwhelmed with argument.with others, even if you don't immediately have a response for them. This just shows how we all need to keep reading, studying, and deepening our faith.