Matthew 9:4

‘And Jesus knowing their thoughts said, “Why do you think evil in your hearts?” '

But Jesus knew what they were saying. Indeed He may well have deliberately provoked it in order to get over to the people that in Him forgiveness had come for all who would turn to God with a view to repenting, turning from sin to God, serving Him and obeying His commandments. For He wanted them to know that in Him their past could be blotted out (Matthew 18:23), and a way was provided for future forgiveness (Matthew 6:12). Indeed Isaiah had made clear that this was God's promise in the time of His Visitation (Isaiah 1:18; Isaiah 43:25; Isaiah 44:22). It was to be included in the task of the Servant of the Lord (Isaiah 53:3; Isaiah 53:10). And indeed it was something that had always been God's offer to men when they turned to Him (Exodus 34:6; Numbers 14:18; Psalms 103:4).

And because of this it was His prerogative as the One Who had come in His Father's Name, as The Son of Man Whom God had established at His right hand to dispense justice and mercy (Daniel 7:14; Psalms 80:17), and had sent to earth (John 3:13) to bring the forgiveness of sins to all who would repent, something that should have been obvious to all from the miracles that He performed. Thus He saw their words as arising out of the evil that was in their hearts. In their prejudice they were refusing to recognise the evidence of the Holy Spirit at work within Him (Matthew 12:28; Matthew 12:31). The casting out of demons was above all the evidence of the Spirit at work, and of the presence in Him of the Kingly Rule of God, which may well be why Matthew puts this incident after the healing of the demoniacs, and they therefore had no reason to doubt His authority as being from God. Indeed what greater proof was needed than that, that God was at work in Jesus? And if He was truly from God, then who could argue that He could not declare God's forgiveness of men's sins.