What does it mean that nothing is covered that will not be revealed, or hidden that will not be known?
There are two views of the statement nothing is covered that will not be revealed, or hidden that will not be known
:
In Matthew 10:26b Jesus encourages the disciples for his command to them in Matthew 10:27 to boldly proclaim the gospel. The phrase means that the secrets of the kingdom (Mark 4:11, Mark 4:22; Luke 8:10, Luke 8:17) must come to light. The gospel, being public, must now be proclaimed boldly, but since the matters promised here are still covered and hidden, they invite objection and persecution, but what cannot yet be seen now will certainly be shown by God to all in due time (see 2 Corinthians 3:12–4:18; Revelation 1:7a).
Matthew 10:26 means that the revealing will be in the judgment spoken of back in Matthew 10:23. While the meaning of the persecution of Jesus’ disciples may still be hidden, it will be seen that a disciple of Jesus Christ was persecuted for the sake of his Master (see also Acts 4:13, Acts 5:41, Acts 9:16; 1 Corinthians 13:9).
Interpretation 1:
In Matthew 10:26b Jesus encourages them with a general principle, from which the command to the disciples in Matthew 10:27 to unashamedly proclaim the gospel flows. The phrase means that all that is secret will inevitably come to light, and when Jesus speaks this, it concerns the very secrets of the kingdom of God (see Mark 4:11, Mark 4:22; Luke 8:10, Luke 8:17). Truth shall always prevail.1
The gospel is God’s good news concerning those blessings in which we come to share through Jesus Christ. That gospel, being public, must now be proclaimed fearlessly. But because the matters promised here are still covered and hidden, they invite objection and persecution. Despite this, Jesus calls upon the apostles to fearlessly continue with their preaching. What cannot yet be observed now, will certainly be seen by all eventually. The apostles proclaim realities that God will manifest in due time (compare 2 Corinthians 3:12–4:18 and Revelation 1:7a).2
Interpretation 2:
This general statement in Matthew 10:26 regarding revealing that which has been covered, needs to be read as a justification of the judgment spoken of already in Matthew 10:23. Behind this hostility are still-unknown motives, and indeed an entire diabolic system. While this may currently still be hidden, it will eventually come to light that a disciple of Jesus Christ was persecuted for the sake of his Master (see also Acts 4:13, Acts 5:41, Acts 9:16 and so on, as well as 1 Corinthians 13:9).3
26 “So have no fear of them, for nothing is covered that will not be revealed, or hidden that will not be known.