Jesus was answering an accusation no one had said out loud. Certain scribes sat "reasoning in their hearts, Why doth this man thus speak blasphemies? who can forgive sins but God only?" (Mark 2:6-7), and Jesus "perceived in his spirit" what they were thinking (Mark 2:8). Anyone can say "Thy sins be forgiven thee," because no one can see whether it happened. But telling a paralyzed man to "Arise" can be tested on the spot. Gill says the question was put "in order to prove his deity," and that both sayings were "easy to say, but not with power and effect." Barnes, writing on the same question in Matthew 9:5, says "neither can be done but by God."

The scribes give no reply, so Jesus answers His own question. "But that ye may know that the Son of man hath power on earth to forgive sins," He turned to the sick man and said, "Arise, and take up thy bed, and go thy way into thine house" (Mark 2:10-11). "Immediately he arose, took up the bed, and went forth before them all" (Mark 2:12). The people "were all amazed, and glorified God, saying, We never saw it on this fashion" (Mark 2:12). The healing everyone could see stood as proof of the forgiveness no one could see.

The scribes were right that only God can forgive sins. That is why they heard Jesus' words as blasphemy (Mark 2:7). Barnes notes on the parallel account that by claiming this power, Jesus "was understood to affirm that he was divine" (Matthew 9:3).

The "bed" the man carried was not a frame bed. The Greek word krabattos is glossed "mat" in the interlinear, and Barnes describes it as probably a mattress or blanket that could be easily carried (on Matthew 9:2). Matthew and Luke record the same question (Matthew 9:5; Luke 5:23). Luke adds that Pharisees and "doctors of the law" were "sitting by," having come "out of every town of Galilee, and Judaea, and Jerusalem" (Luke 5:17).

This question shows who Jesus is. He knew the scribes' unspoken thoughts (Mark 2:8), a power Barnes says "belongs only to God" (on Matthew 9:4). Then He claimed the right that belongs to God alone and backed the claim with a work only God could do. Matthew Henry answers the scribes' reasoning this way: "None can forgive sins but God only; but it is false that therefore Christ cannot."

The order of events matters too. The four men brought the sick man to Jesus, but Jesus spoke first to his sins (Mark 2:5). The visible healing served the invisible gift. Henry writes, "He that could by a word accomplish the sign, could doubtless perform the thing signified." The crowd's response was the right one: they "glorified God" (Mark 2:12).