zealous: This means a strong and sincere commitment to God and to what God desires (see Numbers 25:6–13). This kind of passion can be good and faithful.
In Paul’s time, however, much Jewish zeal was misdirected. Many people did not understand that Jesus Christ is the central point of God’s plan. Because of this, their passion did not lead them to the truth.
Paul points to his own life as an example. Before he trusted Christ, Paul showed great zeal, but it was aimed in the wrong direction (see Acts 9:1–2; Galatians 1:13–14)