Lately I’ve been thinking about some of the contrasts that chase us through life at Emmanuel. They start on Sunday when I walk over the small round disk embossed BOSTON GROUNDWATER TRUST, which is set into the sidewalk in front of the church. It’s one of 800 wells monitoring the groundwater that still covers the 200,000 Maine spruce-tree trunks that were steam-pile driven-in 160 years ago to keep our feet out of the soup below. Sure, I know that part of the motivation for filling the Back Bay was to keep prosperous white Protestants from decamping to the suburbs, and my Irish great-grandfather south of the tracks. But still, there’s no way to get into Emmanuel without at least an unthinking pilgrimage over that magical, invisible, upside-down forest.