But go and learn what this means, I want mercy, and not sacrifice.a For I did not come to call the righteous, but sinners.” Bible
From Hos. 6:6.

“I want mercy, and not sacrifice.” Quoted from Hosea 6:6. See commentary on Hosea 6:6 for more understanding of the why Jesus quoted that verse. Also, he quoted it a second time under different circumstances in Matthew 12:7.

“I did not come to call the righteous.” See commentary on Mark 2:17.

“but sinners.” [For more on Jesus calling sinners to repentance, see commentary on Luke 5:32].

Commentary for: Matthew 9:13