We sit down at a restaurant table, and a waiter lights a candle for us we feel love. We visit a church, see innumerable little flames in front of statue or an icon, and add one more candle, we feel faith. We light Diyas at pooja at festivals even while people pass away.
A flaming candle connects love to love faith to faith and more recently as a sign of protest angst to angst.
What makes the flame something special? It lives. It radiates light and warmth; it moves flickers, flows, jumps and trembles. It seeks sustenance and air. As living beings we compare ourselves to the living flame.