v8-9:
In putting everything under him, God left nothing that is not subject to him. Yet at present we do not see everything subject to him. 9But we see Jesus, who was made a little lower than the angels, now crowned with glory and honor because he suffered death, so that by the grace of God he might taste death for everyone.
Everything is under God's control but at the moment it doesn't look like it from our point of view. So how do we know everything is under His control? Because of Jesus - because He became a man and died on our behalf. That's done, so we know He's in control of everything else. See How can you believe God's in control, by Ben Parker for a more detailed look at this idea.