Never underestimate the little guy. While a minor player in history outside of Ulster County, New York, Isaac and his wife, Maria, were desperately important to Sojourner Truth. And for a very good reason: they were the first to take her in after her escape from John Dumont.
Both Dumont and Van Wagener belonged to the Klyn Esopus Dutch Reformed Church, but had one crucial disagreement. Dumont, obviously, felt slavery was in no way against the teachings of a loving God. The Van Wageners, on the other hand, actually applied logic and were against slavery. They took Belle and her daughter in, encouraged her Methodism and even her preaching, which was beyond unheard of for a newly freed female slave.
When Dumont came to collect his "property"—since Belle didn't even try to hide but openly stayed in the neighborhood—the couple even paid Dumont over $20 dollars for Belle and $5 for Sophia for her housekeeping services for her last year as a slave under the law, letting Isabella settle into mostly free life safely.
While still technically property (and thus given the last name Van Wagner or Wagenen), Belle gained a confidence in herself and her faith that stirred her every move for the rest of her life. That faith shines through in "Ain't I a Woman?"—there's a reason Religion is one of the key themes.