Light is an important image for God. Off the top of my head I think of the psalmist who reminds us that God puts a "lamp unto our feet." Isaiah tells God's people "for those who walk in darkness have been given a great light." Jesus said "I am the light of the world."
Light is important in the story of God. So here in Exodus we see light making its place to show forth God's presence.
We light candles for many of the same reasons above but the candles on the altar for Christians is a reminder that God is present in the meal of Holy Communion. It signifies that within this meal, this candle is lit, on this table, where God is truly present.