They never forgot their past. Moses never forgot how he killed a man in a fit of anger. Paul never forgot how he had savaged the Church of God. Matthew never forgot how, as a tax collector for the Roman Empire, he was considered a traitor to his people.

But God forgot their past. He forgave all their sins and called them to proclaim his mercy. Christians are sinners whom God has mercifully forgiven and called. Only grace can explain why Jesus calls us to faith and promises us salvation. Only grace can explain why Jesus calls his disciples to remember their roots as they serve out his mission of making more disciples of all nations.