On this we must agree to disagree.
Does Christ care about how we believe in Him? Does he care wether we add a few extra lines to the Lord prayer or if we attend Mass or services?
The Lord gave us a clear text on how to live. It is up to each and everyone on how we read and interpret his words.
But I am not a scholar of such things.
I think Christ does care how we believe in him. Think about it. He sent the Holy Spirit to the first believers so they could record his ministry in words. Why? So that all future generations of believers would have those words, and through them the memory of what he said and did. Why go to all that trouble if the words are not important? It makes no sense. And in those words he teaches many things, some that are still hard to accept. He also warned of false Christs, people who would come later and pervert the truth. These false prophets are known by their fruit, and they have no future with God, other than to wait for judgment.
So you see, unless one is trying to be a false prophet, it is not up to everybody to cast their own private filter over the teaching of Christ, picking and choosing what they like, and ignoring the rest. When he teaches for example that Gods design for marriage consists of a man and a woman in permanent union, he implies that God did NOT design the alternatives to that arrangement conceived by the warped mind of sinful humans. Or by affirming the authority of the commandments, he rejects idolatry, lying, stealing, adultery, coveteousness (aka greed), etc. Most importantly, by establishing faith in him as the sole basis for human redemption, he excludes all alternative schemes for human salvation.
Furthermore, he, in his own words, taught that to reject him as the Son was to reject the Father. If his words mean anything at all, they mean that a) we cannot look to our own man-made religious divisions as the source of our salvation, and b) neither can we just make stuff up about him and hope for the best. God is not mocked. What we sow we will reap. If we sow a foolish unwillingness to learn and obey his words, we will reap self-deception, error, and harm to ourselves and others. If we sow an earnest desire to know and obey him and the doctrine he gave us in his words, then we will know truth, and that truth will free us, and we will be that tree that bears good fruit.