Invoking images of the Crucifixion and singing about "drops of blood rolling down the street" has to be one of the least likely ways to start a set at a blues club. Nonetheless, when singer Mighty Sam McClain took the stage at the House of Blues in Harvard Square last Friday night, he began by testifying over the horn-powered sound of his seven-piece band. In a white Nehru suit, McClain played a dual role that certain bluesmen, like the great Delta artists Charlie Patton and Son House, have assumed since the music’s beginning — that of preacher and entertainer.

Mighty Sam didn’t so much cross those lines as erase them, exhorting us in his songs and his stage patter both to have a good time and to accept Jesus. "Here I Come Again," which arrived after his opening sermon, was a bouncy up-tempo statement of intent. His burnished voice, seemingly as elemental as fertile Southern soil, boomed with lionine strength as the song announced his presence and his determination to persevere. Then he kicked his band into a strutting Hi Records–style groove for "No One Can Take Your Place" — which doubled as a pledge of love for his wife, Sandra, and an affirmation of his religious beliefs — before heading back to the pulpit for his epic number about tested faith, "Hanging on a Cross (Between Heaven and the Blues)."

Faith and perseverance have become the dominant themes of McClain’s career in recent years. Following a late-’80s comeback, he has taken control of each aspect of his career in the course of making a series of rich albums. He’s become a prolific songwriter intent on steering his tunes along a spiritual path; at the same time he’s gradually assumed responsibility for his own booking, management, tour structure, and publicity. Several months ago he took another step in empowerment when he left his long-time label, Telarc, and self-produced his next CD, One More Bridge To Cross, which will see international release early next year on his own Mighty Music label. Given that McClain has struggled for his art since the ’60s, when his recording of the Patsy Cline hit "Sweet Dreams" made him a brief R&B sensation, and that he endured the pressures of the Jim Crow South as a young man, his current self-made success amounts to an act of personal transcendence.

He’s likely to keep crossing new bridges as he encounters them. But recently he built one to his past. After seeing a photo of singer/guitarist Little Melvin Underwood in a blues magazine this year, McClain reached out to the man who gave him his start in show biz — as his valet — in Louisiana in the early ’60s. At the House of Blues, Underwood took the stage with McClain’s band for a few warm-up tunes. He proved an affable sparkplug as he plucked fat notes from his guitar and sang "Kansas City" and "Sweet Black Angel" with a raw desire to entertain that bared his early chitlin-circuit roots and rekindled, for a few minutes, the spirit of the time and the place where Sam McClain first became Mighty.