through - literally, “by the hand of,” that is, by the agency of.
branches - literally, “ears”; so the olive branches are called, because as ears are full of grain, so the olive branches are full of olives.
golden oil - literally, “gold,” that is, gold-like liquor.
out of themselves - Ordinances and ministers are channels of grace, not the grace itself. The supply comes not from a dead reservoir of oil, but through living olive trees (Psa 52:8; Rom 12:1) fed by God.