When someone says, "I believe in what you say, not what I hear," they are expressing a level of trust and faith in the person they are addressing, rather than relying on rumors, gossip, or hearsay from others. It means that they place greater importance on the direct communication and information received from that particular individual than on secondhand or indirect information.
By saying this, the person is emphasizing that they value the speaker's credibility, honesty, and firsthand knowledge. They may have a strong bond or relationship with the speaker, which leads them to prioritize their perspective over what others might be saying about the same matter.
This expression can be used to convey trust and a willingness to consider the speaker's viewpoint as more reliable and meaningful than any rumors or information received from other sources. It's a way of demonstrating loyalty and belief in the person's integrity.