Channing's sermon of 1828, Likeness to God, presses further than the Baltimore statement and is the point at which the older liberalism reaches its edge. Its argument is that we know God only through the moral and spiritual capacities we find in ourselves, that these are genuinely divine in kind rather than merely analogous, and that religion consists in their unfolding. Human nature, so far from being depraved, contains the material out of which any true idea of God is built.
The younger writers read that and drew a conclusion Channing did not. If the divine is known through the individual soul, they asked, what work is scripture still doing, and what is the standing of the miracles Unitarians still defended as the evidence of revelation? Emerson's Divinity School Address of 1838 answered by discarding the evidence and keeping the experience, and the Transcendentalist controversy that followed split the liberal camp Channing had assembled.
His own position on that quarrel was uncomfortable. He was sympathetic to the young men personally and unwilling to follow them, and he died in 1842 before the argument settled. In his last years he turned increasingly to slavery, publishing against it from 1835 at real cost to his standing in commercial Boston, and it is that work, rather than the doctrinal controversies, that his own denomination now tends to remember first.