The apostle Paul lamented the spiritual condition of his fellow Jews and expressed his concern in a moving piece to the church in Rome: "Brothers, my heart's desire and prayer to God for the Israelites is that they may be saved. For I can testify about them that they are zealous for God, but their zeal is not based on knowledge. Since they did not know the righteousness that comes from God and sought to establish their own, they did not submit to God's righteousness. Christ is the end of the law so that there may be righteousness for everyone who believes." (Romans 10:1-4) The problem experienced by these God-believing Jews was that they did not know how God reconciles sinners to himself. They didn't know that through the atoning sacrifice of his Son, God pardons sinners; as a result they tried, by their own efforts, to set themselves right with God. Their sincerity could not be questioned, but they were engaging in a futile exercise – trying to save themselves. If a lifeline of hope could be offered to people who are zealous for God, but unconverted to Christ, it would have been here. But no such hope is given.
There are many Christians in the same situation as the Jews of Paul's day. They believe in God, they believe that Jesus is the Son of God, they believe he was born of a virgin named Mary, that he died and rose again from the dead. But they have never turned their lives and their trust completely over to the Lord Jesus Christ. And without conversion one cannot be reconciled to God. We must remember that the Jews were not lost because they did not believe in God, but because they did not totally trust their life to the atoning sacrifice of Jesus.
It is the duty of the church to evangelise, and evangelism must take place not only among the world's unbelievers, but also among the multitudes of unconverted believers.