What happened next evidently took place in heaven.
6:9 The altar John saw was evidently in heaven (cf. 8:3, 5; 14:18). Earlier John had seen a throneroom in heaven (chs. 4-5), but now he saw a temple. Probably the concepts of palace and temple communicate aspects of God's magnificent dwelling-place in heaven (cf. Ps. 11:4; 18:6; 29:9-10; Isa. 6:1: Hab. 2:20). This altar was evidently an altar of sacrifice rather than an incense altar (cf. 5:8; 8:3-5; 14:17-18). Under this altar were the souls (Gr. psyche, lives) of people who had died for their faith in God and their faithfulness to Him during the period just described (vv. 3-8; i.e., in the Tribulation so far). Perhaps the idea is that the lives of these martyrs were sacrifices to God (cf. Phil. 2:17; 2 Tim. 4:6). The "and"(Gr. kai) is again probably ascensive (cf. 1:2, 9) meaning the word of God "even"the testimony they maintained.
These people must be those who died after the Rapture since all Christians living at the time of the Rapture will experience bodily resurrection and go directly into Jesus Christ's presence then (1 Thess. 4:16-17). Consequently the people John described in this verse are evidently those who come to faith in Christ after the Rapture (cf. Matt. 24:9; Luke 21:11). They became believers during the first half of the Tribulation and then suffered martyrdom for their faith. John did not see their resurrected bodies because God had not resurrected them yet. The resurrection of Tribulation saints will not occur until the end of that seven-year period (cf. 20:4).
6:10 John saw these martyrs calling out to their heavenly Master (Gr. despotes) to punish their murderers.259"Master"implies divine might, majesty, power, and authority, and it stresses the absolute power of God.260How much longer did they have to wait for God to avenge them (cf. Ps. 79:10; 94:3; Hab. 1:2)? "Holy and true"were attributes of Christ earlier (3:7), but here the Father is probably in view since He is the source of the judgments. "Those who dwell on the earth"is almost a technical expression in Revelation describing unbelievers who are hostile to God (cf. 3:10; 8:13; 11:10; 13:8, 12; 17:2, 8).
"Their prayers for revenge upon their enemies are viewed as the fifth judgment against the earth-dwellers."261
6:11 Each martyr received a long white robe (Gr. stole). They had been faithful and had suffered martyrdom for their fidelity to Christ (cf. 3:5; 7:9, 14). God told these martyrs to be patient. More people would experience martyrdom before it would be God's time for Jesus Christ to return to the earth and judge their living adversaries.