I enjoy reading the sermons and hymns of Benjamin Beddome, an 18th century Reformed pastor. Recently, I came across the following quote which deeply struck me. Although Beddome was preaching on the faithfulness of God, these words are part of his conclusion. To me, they present solid motivation for believers to share the Gospel with the lost as well as an appeal to the lost to believe the Gospel.
"Whilst saints rejoice, let sinners tremble at God's faithfulness. As God is faithful to his promises, so is he also to his threatenings. He is as unchangeable in his wrath as in his mercy."