That is a key difference, yes, and was the cause of debate in the early church. Since all of the early believers were Jews, it was natural for them to bring adherence to the law with them into Christianity, but when Gentiles started coming to faith, they realized it was not right to put the Law on them.
One thing I would like to stress is that faith is much stronger than mere belief. Example: a daredevil walks across Niagara Falls on a rope and the crowd oohs and ahhhs. He comes back, puts a wheelbarrow on the rope and makes the crossing again, pushing it in front of him. On his return, he asks the crowd, "How many of you believe I could put one of you in this wheelbarrow and safely push you over and back on the rope"? Several hands go up. "Okay, which one of you will get in the wheelbarrow"? Belief is saying, "Sure, you can do that". Faith is getting in the wheelbarrow. IOW, when a Christian professes faith in Christ, he/she is saying a whole lot more than just "I believe", he/she is saying, "I trust completely in Him and I put my life in His hands".
Now, God seeing the heart and actions are not in opposition. We Christians focus on the heart because Jesus ELEVATED the tenets of the Law from actions to attitudes and thoughts. To paraphrase what he said, "The Law says do not murder. I say that if you are angry with your brother, you are liable for judgement. And again, the Law says do not commit adultery. I say that if you look at a woman with lust, you have already committed adultery with her in your heart". Now, if it is impossible to 100% keep all 613 commandments when they are action based, think of how much harder it is to keep your thoughts totally free of sin.
That is why I say that God sees the heart where the true character lies. You can fool people by acting piously and obeying the rules on the surface, but God sees the reality. Are you familiar with the way Jesus reacted to the Pharisees of His day? He called them whitewashed tombs, pretty on the outside but dead on the inside, because on the surface they followed the Law meticulously, but on the inside were selfish and out to obtain glory for themselves, not God. Actions are very important, make no mistake about that, but we believe that actions follow the dictates of the heart. If you are an angry person inside, for example, you can be nice and polite for only so long before that anger comes out.
Finally, I apologize for making you feel insulted. I hope we can have a good discussion.