13:9 God and John called on the readers of this book to pay attention. Particularly those living at this time in the future should do so. Note that John made no reference to "the churches"as in similar exhortations in chapters 2 and 3 (2:7, 11, 17, 29; 3:6, 13, 22). This supports the fact that Christians (i.e., believers living in the church age) will not be present on the earth at this time (3:10). It is what follows (v. 10) that this verse announces, not what has preceded.
13:10 God promised the saints that those He has destined for captivity (i.e., Antichrist, his followers, and the saints) will eventually end up as captives (cf. Jer. 15:2; 43:11). Those who kill others (the others being believers in Jesus Christ, v. 7) will die (cf. Matt. 26:52). This assurance that God will execute justice should encourage the saints to persevere steadfastly and to trust God during this period of intense persecution and martyrdom (cf. 14:12). The whole verse is an encouragement for believers to submit to the sovereignty of God realizing that He has permitted Antichrist's activity but that they are secure. It also assures them of divine retribution and urges them to persevere faithfully.