Priests and prophets could announce forgiveness granted by God, but the scribes hear Jesus' personal pronouncement as an intrusion upon a divine prerogative.
Mark makes their theological objection central rather than incidental.
The LORD is repeatedly described as the one who forgives iniquity and removes transgression. Psalm 103 praises God as the one who forgives all iniquity, and Isaiah 43:25 emphasizes God's own act of blotting out sin.
Daniel 7 also supplies background for the Son of Man's extraordinary authority, a theme Mark will develop toward Jesus' trial.
Jesus first addresses the man's sins rather than his paralysis. When the scribes reason that he is blaspheming because only God can forgive sins, Jesus knows their thoughts and confronts the objection.
He then heals the paralytic expressly so that observers may know that the Son of Man has authority on earth to forgive sins. The visible act validates the invisible claim.
Mark allows the objection 'God alone' to stand and then shows Jesus exercising the disputed authority rather than withdrawing the claim.
The episode is therefore strong evidence of Jesus acting with a prerogative belonging to God, while the larger Gospel explains how the Son of Man relates to the Father who grants and vindicates his authority.
The scribes accuse Jesus inwardly of blasphemy; the crowd is amazed and glorifies God after the healing.