Source identified1
“Self-reverence, self-knowledge, self-control, These three alone lead life to sovereign power.”
Tennyson joins respect for oneself with knowledge and restraint: durable personal power is presented as the result of living by an inward law rather than seeking power merely for its own sake.
Source note: Oenone, in The Early Poems of Alfred, Lord Tennyson, Project Gutenberg #8601. Pallas speaks the lines while arguing that self-reverence, self-knowledge and self-control lead to a life governed by right rather than by reward; this is poetic character speech, not a prose maxim detached from the poem.