Jesus forgives a man merely because of his faith. But forgiving a man's sins is something only God can do. Jesus proves his deity by healing the paralyzed man.
New King James Version (NKJV)
Jesus Forgives and Heals a Paralytic
9 So He got into a boat, crossed over, and came to His own city. 2 Then behold, they brought to Him a paralytic lying on a bed. When Jesus saw their faith, He said to the paralytic, “Son, be of good cheer; your sins are forgiven you.”
4 But Jesus, knowing their thoughts, said, “Why do you think evil in your hearts? 5 For which is easier, to say, ‘Your sins are forgiven you,’ or to say, ‘Arise and walk’? 6 But that you may know that the Son of Man has power on earth to forgive sins”—then He said to the paralytic, “Arise, take up your bed, and go to your house.” 7 And he arose and departed to his house.
8 Now when the multitudes saw it, they marveled[a] and glorified God, who had given such power to men.
- Matthew 9:8 NU-Text reads were afraid.