Matthew 9:4 - Albert Barnes' Notes on the Bible

Jesus, knowing their thoughts - Mark says, “Jesus perceived “in his spirit” that they so reasoned.” The power of searching the heart, and of knowing the thoughts of people, belongs only to God, 1 Chronicles 28:9; Romans 8:27; Revelation 2:23; Jeremiah 17:10. In claiming this, as Jesus did here, and often elsewhere, he gave clear proofs of his omniscience, John 2:24-25.