Why sincerity is not enough
I used to be one of them. You know the kind of person? They think that they are basically good folk trying their best. They are not sure who God is and don't think it really matters. After all, if I am sincere in my belief surely God, whatever god there is, will honour that?
It is a question many ask even in the church: "Why do we need to come explicitly through Jesus? Why can't God save through other religions if the person is sincere?" The problem with this kind of question is that it has the primary end of salvation all wrong. We want to think that salvation, in so far as we think there is the need to be saved, is all about us, but it isn't. I will come back to that in a moment.
But first, let me address the "Why do I need to be saved at all?" question. It is an important one. If I am basically good, and do good things, then surely the good outweighs the bad? The trouble with this is that it ignores the real problem. The problem is that God created us to be in his image. We were to be dependent upon him for light and life and happiness. And we were to glorify him. When we seek to be autonomous, independent from God, we cease to be the full humans we were created to be. We lose the spiritual life blood that comes from our communion with God. Further, our decision to be independent is a desire that god were not actually there. Or if he is, that he becomes a servant for our felt needs. "When I am in trouble I always pray that God will get me out of it." We make God into Aladdin's genie, a slave to our wishes. And that is to try and knock him off the throne and put ourselves there instead. Do you see? Any relationship where one expects the other to provide for him is one in which the one expecting, whether consciously or not, is placing him or herself in a position of authority over the one that is expected to provide. It is also saying that that person doing the expecting knows better than the provider what ought to be provided. And in all of that, what we are doing is rebelling against the rule of the most powerful being in the universe. And that's actually not such a smart idea. Especially when he declares that such rebellion will meet with the fulness of his anger. At which point the words of the Italian Captain from "Allo, Allo" come to mind, "What a mistake-a to make-a."
And it is this that we need saving from.
So, to return to the other question: Why do we need to go through Christ?
(i) God's anger against sinners needs to be turned away from us if we are to have any hope. But we are so shot through with sin that we can do nothing to bring that about. Even if we were able to fully obey God in every way (including loving him with all our hearts, minds, bodies perfectly all the time; and loving our neighbour as ourselves, perfectly, all the time), which we cannot, we would only be doing what we ought to do anyway. We would not be able to make good the sin we have already committed. But Jesus' sin bearing death deals with that for us. In him our sin is judged so that we need not face the penalty.
(ii) Salvation is not ultminately about us, although God does love us, call us, draw us, and design for us the greatest happines. But that greatest happiness is to be found in the ultimate end of salvation. It is about Jesus. Colossians 1 tells us that all things were made for Christ and that the goal of history is that all things will be brought together under him. That includes you and me. God the Father wants to glorify his Son in the salvation of sinners. We are given to Jesus from the Father (John 6:37). Any means of salvation that by-passes Jesus would not glorify or honour him. Christ, as the eternal Son made flesh, is the object of his Father's love and he desires no less than that he be glorified in all creation. The Son also wants the Father glorified (John 17:1) and the Father is glorified when saved sinners delight in all that he is for them in Christ Jesus (as John Piper puts it).
Therefore, one cannot sincerely seek salvation outside of Christ. First because you will not be seeking to be saved from sin by God's grace, but will be continuing to save yourself by your own efforts. And that, of itself, is sin. Why? Because to act independently of God is the very essence of sin. Second, and related to it, if one is coming by other means than Christ one is, by that very act, rejecting Christ. He said that he is "the way, the truth and the life." He also said that "No one comes to the Father except through me." (John 14:6). To try and get to God through any other means, therefore, is to reject Christ because you are saying you think he is lying on this point. And it is a denial of the glory of Christ to imagine that sin blinded men and women (however sincere they may be) groping around with false gods might be allowed to by-pass the one whose glory they so clearly reject. And notice that the gospel (the good news) is called "the gospel of the glory of Christ, who is the image of God." (2 Corinthians 4:4).