Imagine that the three candles in the photo are the Father and the Son and the Holy Spirit, while the flame is the divine substance or nature. The three candles fully participate in the same flame, as the three persons of the Trinity fully participate in the same and indivisible divine substance. Of the three candles, two received the flame from the first. In the Trinity, the Son and the Holy Spirit received their essence and their subsistent being from the Father.
Cristiani Cattolici Romani 