The Jews who did not believe in Jesus claimed with those words that Jesus was taking a power that only God has. But God and Jesus work together. Jesus does not do anything except what his Father allows.
And look! men were carrying a paralyzed man on a stretcher, and they were trying to bring him in and place him before Jesus+ 19 So not finding a way to bring him in because of the crowd, they climbed up to the roof, and they lowered him on the stretcher through the tiling, right among those in front of Jesus. 20 When he saw their faith, he said: “Man, your sins are forgiven.” 21 Then the scribes and the Pharisees started to reason, saying: “Who is this who speaks blasphemies? Who can forgive sins except God alone?” 22 But Jesus, discerning their reasoning, said in answer to them: “What are you reasoning in your hearts? 23 Which is easier, to say, ‘Your sins are forgiven,’ or to say, ‘Get up and walk’? 24 But in order for you to know that the Son of man has authority on earth to forgive sins—” he said to the paralyzed man: “I say to you, Get up, pick up your stretcher, and go to your home.” 25 At that he stood up before them, picked up what he had been lying on, and went to his home, glorifying God. 26 Then one and all were seized with amazement, and they began to glorify God, and they became filled with awe, saying: “We have seen wonderful things today!”
28 Jesus then said: “After you have lifted up the Son of man, then you will know that I am he and that I do nothing of my own initiative; but just as the Father taught me, I speak these things. 29 And the One who sent me is with me; he did not abandon me to myself, because I always do the things pleasing to him.”
Jesus was prophesied to be one who can do this:
11 Because of his anguish, he will see and be satisfied.
By means of his knowledge the righteous one, my servant,
Will bring a righteous standing to many people,
And their errors he will bear.
So Jesus was given this holy spirit and power to do his Father's will, including forgive sins.