While attending Trinity Evangelical Divinity School in Deerfield, Illinois, Mack read of the church’s exodus from the inner city and visited ministries in Chicago. He and Joan committed themselves to return to the black church, community, and public schools.
In 1969 they moved into Chicago’s West Side and began attending Keystone Baptist Church. In 1972, Mack was appointed by Missions Door to pioneer a ministry to black students in the Chicago area.