Hebrews 12:1 says, "Therefore, since we are surrounded by so great a cloud of witnesses, let us also lay aside every weight, and sin which clings so closely, and let us run with endurance the race that is set before us."
What does this mean, that we are surrounded by a great cloud of witnesses? Well, it's often interpreted that the saints who have gone before us, the faithful who have died and are with Jesus in heaven, are looking down from above. They're watching us, cheering us on as we run the race, just like athletes in a sports arena would compete in front of a big crowd.
However, no where else in the Bible are we given a picture of saints watching us from heaven. Furthermore, the Bible doesn't say anywhere that we should pray to these believers. They're not watching, and we can't talk to them.
So they're not witnessing us. They witness to us. The stories of these saints and their completed lives of faithfulness continue to minister to us through the Scriptures. These witnesses were just named in the previous chapter.
Saints like Abel, Enoch, Noah, Abraham, Sarah, Isaac, Jacob, Joseph, Moses, Rahab... "And what more shall I say? For time would fail me to tell of Gideon, Barak, Samson, Jephthah, David, Samuel and the prophets" (Hebrews 11:1-40), many other men and women, who by faith finished the race and won the prize.
And so, by their witness, we learn to put off sin and run the race, pointing us to Jesus, the founder and perfecter of our faith. And as we are perfected in our faith by the testimony of the saints who went before us, so they are perfected also:
"And all these, though commended for their faith, did not receive what was promised, since God had provided something better for us, that apart from us they should not be made perfect. Therefore, since we are surrounded by so great a cloud of witnesses, let us also lay aside every weight, and sin which clings so closely, and let us run with endurance the race that is set before us, looking to Jesus, the founder and perfecter of our faith, who for the joy that was set before Him endured the cross, despising the shame, and is seated at the right hand of the throne of God." Hebrews 11:39-12:2...until we are all presented together before God as the purified bride of Christ, when we understand the text.