On February 10, 1900, Kerr said that he was "called" to be pastor of the First Presbyterian Church in Tulsa, a small village in Creek Nation, Indian Territory.
The church, founded in 1885 by European Americans and served mostly by itinerant ministers, was located at the crossing of the Frisco and Midland Valley Railroad tracks.
As a missionary, Kerr frequently went to Tulsa's "skid row" on First Street to pray, kneeling in the gutter with drunk cowboys on Friday and Saturday nights to lead them to Christ.
The Kerrs found their original missionary vocation to the Creek and Freedmen of the town developed into serving an all-white church.
On the afternoon and evening of May 30, 1921, a large crowd of white people began assembling outside the Tulsa County Courthouse at 6th Street and Boulder Avenue.
After discussing the situation with his family, Kerr responded by going to the courthouse and pleading with the would-be lynch mob to go home.
On his own, Kerr opened the church basement to temporarily house refugees from the violence and destruction, helping mostly women and children.
The white mob attacked blacks and burned down much of Greenwood, which had been so successful economically that it was called the "Wall Street of the West."
[4] Implementation of the Dawes Act of 1877 had resulted in former land reserved for Indians being declared surplus by the federal government and being released for homesteading to non-Native Americans.
Having personally witnessed Indians being swindled out of their lands and rights by abuse of whiskey, Kerr became the foremost temperance crusader in Oklahoma.
[citation needed] Kerr's sense of social justice led him to sponsor an annual Labour Day service for all trade union members at Tulsa's First Presbyterian Church.
[citation needed] Kerr held annual summer tent revivals in the vacant lot next to the Tulsa County Courthouse.
[citation needed] Kerr often brought food and clothes to, prayed with, and found jobs for the many homeless people (Black, white, and Indian), living under Tulsa's 11th Street Bridge.