Initially in 1860, he began studies in the Preparatory program as a junior student and progressed to senior standing the following year.
It was in the literary society that Sellers was able to hone his oral and written communication skills as he debated his fellow students on topics ranging from economics to ethics, such as the lawfulness of slavery.
During his junior year at Wheaton College, Sellers joined several of his classmates and heeded the call of the Union Army for "hundred-days men."
This regiment was organized at Camp Fry, Chicago, Illinois, and mustered in for 100 days service from June 1, 1864. and encamped and trained near Paducah, Kentucky – not far from his Shawneetown home.
With the help of Wheaton's president, Jonathan Blanchard, Sellers moved to Boston and enrolled at Andover Theological Seminary.