what might explain the close connection between calls for religious revival and campaigns for social reform in the 1830s and 1840s

The Christian believers that got involved in religious revivals firmly believed that the Second Coming of Jesus Christ would take place by the end of the 19th century. Because of that, they considered that all the evils of society needed to be fixed in order for society to be perfected so that it would be ready for the Second Coming of the Lord. Being Christian, they naturally considered that Christian ethics needed to be applied to all society's problems (crime, greed, alcoholism, lust, poverty, slavery, etc.) for that purpose.