A - Thanks for the question. As you said further in your email - "it is a huge question" and I agree. This is one of those big questions that seem to poke up at us at one time or another. I hope I can do justice in my answer to the seriousness of your question.
What I might do first is to assure you that it isn't an impossible task that God has set before us - to know about Him, His creation and His revelation to us. Otherwise, God has created us to be uncertain of His plans for us. But, before I go on I want to state a few things:
1 - Humans make mistakes, God does not.
2 - Human knowledge is limited, God's knowledge is not.
3 - Human faith is imperfect and is made unnecessary once we reach heaven and see God face-to-face.
4 - To believe in God, as revealed through Christ, is rational.
5 - Our understanding of God is limited and imperfect - but this does not mean we cannot know what He has revealed to us - otherwise He is a bad teacher.
I would like to also affirm that you are correct in saying that if a person worships and believes in the one God, then they are (in some imperfect way) worshiping and believing the one true God. This is why the Catechism says:
The plan of salvation also includes those who acknowledge the Creator, in the first place amongst whom are the Muslims; these profess to hold the faith of Abraham, and together with us they adore the one, merciful God, mankind's judge on the last day. (CCC 841)They may not understand the nature of God correctly, but they still adore Him. In fact, the Church acknowledges and lifts up the truths that are found in other religions:
The Catholic Church recognizes in other religions that search, among shadows and images, for the God who is unknown yet near since he gives life and breath and all things and wants all men to be saved. Thus, the Church considers all goodness and truth found in these religions as "a preparation for the Gospel and given by him who enlightens all men that they may at length have life.(CCC 843)Now, this does not mean that all religions are the same or that we are incapable of knowing truth. To say this is a relativistic outlook. Relativism is the philosophical belief that truth cannot be known objectively because it is relative to a person, place, time, situation, etc. But, this is a contradiction in and of itself - because we cannot reject objective truth by stating an objective truth.
Is Christianity true? Well, first we have to define what we mean by "true". Truth is that which corresponds to reality. So, we would say that other religions are partly true, but not fully so. Only Christianity has the Truth of the nature of God - found in the Trinity and the Incarnation of Christ. Where contradictory truths are taught (e.g., Jesus is God vs. Jesus is not God) then both cannot be true.
The claims of Christianity are exclusive:
- Either Jesus is God or He isn't.
- Either God revealed Himself to us through the Sacred Scriptures and Tradition or He didn't.
- Either God gave real authority to the Catholic Church or He didn't.
There are many more claims, but these will suffice for our answer here. Are these claims true? Well, I can prove them partly - in that I can show they are rational and believable. Whether or not an individual decides to accept these propositions is an act of faith - not just intellect.
I disagree with you on one point. God did give us the power to know Him personally by revealing Himself to us.
- He reveals Himself to us in several different ways and on different levels. He reveals his existence to us through creation. Aristotle believed in a creator - yet he didn't have any kind of special revelation given to him.
- He reveals Himself to us through our consciences. We know that we are supposed to do good and avoid evil. This is the voice of God within.
- He reveals Himself to us through others. Have you held a baby in your hands or had a person comfort you? This is God's work.
- He most explicitly and especially reveals Himself to us in the extraordinary way of giving us Sacred Scripture and Tradition.
This isn't putting God "in a box" but rather stating that God isn't a liar and that according to the nature of truth, He truly reveals Himself to us. If we get specific, we can see this is true. So, answer these questions:
- -Did Jesus exist? No historian worth his salt denies this.
- -Did the apostles die for their belief in Him? Again, yes.
- -Did they die for the truth that He was God or a lie? The logical answer is that it is for truth.
I myself have experienced Christ and I know Him personally, so the truth of my faith does nothing that is contrary to reason, but goes beyond the limits of reason. Being a Christian isn't about us searching for God, it is about God searching for us.
It isn't about being triumphalistic, exclusive or arrogant about truth. Christ claimed He was God, He can't both be God and not be God. I choose to believe, by the weight of evidence and guided by faith. But, remember that we are not saved because of our knowledge of God, but our faith in God. Thus, the Catholic Church, while it claims to have the fullness of the means to grace and truth - does not claim that you have to be (explicitly) united to the Catholic Church for salvation.
As for cultural perceptions changing truth - this boils down to cultural relativism - as if truth were subject to cultures. The Church does teach that the means in which we speak about God might change somewhat from culture to culture - but the underlying truth is the same. For instance, Catholics in Africa frequently dance to praise God. But, because of the implications of what dancing means in our western culture, we do not have liturgical dancing here. This is an application of the same truth - that we worship with both body and soul. But, the truth isn't different because of cultures. If that were the case, then once again, God is a bad teacher.
There are many good books that answer, in more depth than I did here, these questions. I will recommend two to you:
1 - Mere Christianity by CS Lewis
2 - Handbook of Christian Apologetics - Kreeft and Tacelli
I hope this helps in some small way.