Dear Mary:

One of the common mistakes that people make in reading the Bible is to presume words and phrases have the same meaning as we think of them in the 21st Century -- they do not necessarily.

For the ancient Jews is was common to try to describe the attributes of God (and common for us today) in words that reflect human behaviors or emotions. It is a way we can understand what we cannot fully understand. This is why the ancient Jews used the phrase "jealous God" in passages such as Exodus 20:5.

The phrase cannot mean that God had the human emotion of jealousy. God is the Creator and is Pure Spirit. He does not have human emotion (which is biologically and psychologically based) that seeks to emphasize the uniqueness of God. The phrase, rather, is an anthropomorphism, in this case, to emphasize the uniqueness of God.

To quote from the Navarre Bible Commentary (one of the best available):

Since he is the only true God, he cannot abide either the worship of other gods (cf. Exodus 34:14) or worship of idols. Idolatry is the gravest and most condemned sin in the bible (cf. Catechism of the Catholic Church, 2113).

Therefore, the phrase "jealous God" merely means that God expects His children to acknowledge Him as the True God and the only True God (which He is). To seek after false gods is therefore sin and sin reaps its own reward.

God bless,
Bro. Ignatius Mary