Hebrews 12:1

NIV
Therefore, since we are surrounded by such a great cloud of witnesses, let us throw off everything that hinders and the sin that so easily entangles, and let us run with perseverance the race marked out for us.
KJV
Wherefore seeing we also are compassed about with so great a cloud of witnesses, let us lay aside every weight, and the sin which doth so easily beset us, and let us run with patience the race that is set before us,

The great cloud of witnesses is not referring to actual people who are watching us; but witnesses and examples of those who have testified to the truth of the faith.

The Book of Hebrews was an encouragement to the Hebrews, who had left Judaism to follow Christ. They were facing severe persecution. The writer wants to communicate that their suffering is not unique, but part of the great marathon.

The Christian life is a marathon full of hills, bad weather, green pastures, and sharp turns. In order to keep our endurance strong, we need to strip ourselves on anything that separates from God, especially sin. When we free ourselves of the baggage that entangles us, we can stop tripping over our sin and run freely toward the prize of Heaven.
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