What does Revelation 6:3 mean?

We read in this verse that when the Lamb opens the second seal (Revelation 5:1–7), the second living creature issues the command to come forth.

In this passage, every time a seal is broken, John sees what transpires on earth. This begs the question: can people in heaven see what is happening on earth? This is also suggested by statements such as Jesus saying there is rejoicing in heaven over one sinner that repents (Luke 15:10). But do the angels actually see the sinner repent, or is the repentance reported to them? Hebrews 12:1 states that we are surrounded by a great cloud of "witnesses." Some suggest these witnesses behold our lives from heaven. However, that verse refers to the believers cited in Hebrews chapter 11; it implies that those examples are evidence—witnesses—of the truth being explained in that passage. In addition, we do not know that John was literally in heaven at this point. He may have beheld what was transpiring on earth in a vision he received from the Holy Spirit.

We can be sure, though, that God sees everything that transpires on earth because "no creature is hidden from his sight, but all are naked and exposed to the eyes of him to whom we must give account" (Hebrews 4:13).