Message encryption provides confidentiality. Allows users to encrypt document with the public key which can be decrypted only with the corresponding private key. To put it in simple terms when encrypting, you use their public key to write message and recipient uses their private key to read it. One of the most secure way protecting confidential documents.
Message signing binds the identity of the message source to this message. It ensures data integrity, message authentication, and non-repudiation altogether. When signing, you use your private key to write message’s signature, and they use your public key to check if it’s really yours.