Believing in is simply believing that

". . . Some people find a great difference between believing a person and believing in him. there is no doubt a difference, but it is quite different from the difference these people think they have in mind. Attentive readers who read their publications will conclude that very likely they have nothing in mind, for they regularly avoid stating what the difference is. Let us use a human example, for if we begin by talking about believing in God, our sense of piety may deceive us. Any ordinary instance will do. I meet a stranger on the plane and we begin to talk. His conversation indicates that he is a chemical engineer. Somewhere along the line he remarks that a certain chemical process does so and so. I believe him; I accept his statement as true. But I do not for that reason believe in him. He may be a scoundrel. Occasionally engineers are. On the way home I sit next to some legal matter. But now I not only believe this one statement: I believe in him because I believe that anything he will tell me in the future, especially if it concerns law, will be true. I believe he always tells the truth and always will. Of course, since he is a sinner, he may make a mistake. But when we believe in God, we believe that he will never make a mistake. To believe in is simply a reference to the future beyond the present single statement." - Gordon H. Clark, Faith and Saving Faith