Truth, in this poem, could also be the truth of God. We know Dickinson was a religious person and definitely believed in the Christian God. Just as the truth is revealed bit by bit in this poem, so could the proof of God. And Dickinson hints at this with light imagery (going to the light at death is considered being pulled up to heaven by God), and the mention of children. In Christian religions, God's constituents, or believers, are often called his children ("peeps" is a distant second).
Even if truth isn't a metaphor for God in this poem (and we think there's enough evidence to link the two), Dickinson's Christian education and upbringing is certainly shining through here. (Light? Shining? Anyone? Is this thing on?)