Ezekiel 3:18?

While Reformed theology does teach that God, by his eternal decree (according to the unsearchable counsel of his own will), predestines some to eternal life in heaven and the rest to eternal wrath in hell, it also teaches that God carries out that decree by secondary causes. God, in his providence, makes use of means, namely the preaching of the gospel, to carry out his divine will in terms of who will be saved and who will not (see WCF 3 and 5).

In Romans, after explaining the manner in which people generally come to faith in Christ (Rom. 10:9-13), Paul explained the means by which people are usually saved. Specifically, he said that they are saved through the presentation of the gospel by other people (Rom. 10:14-15). Paul taught that unless believers in Christ proclaim the gospel to others, no one else will be saved. We, as Christians, are the ones ordained by God to carry out his divine will of bringing the elect to faith.

Ezekiel 3:18 does not teach that Christians will lose their salvation if they do not preach the gospel to unbelievers. But it does teach that we are responsible for preaching the gospel to unbelievers, and that we sin when we fail to do so. We should make it "our goal to please [the Lord], whether we are at home in the body or away from it. For we must all appear before the judgment seat of Christ..." (2 Cor. 5:9-10). Therefore, as Paul implies and Jesus commands, "Go and make disciples of all nations" (Matt. 28:19).