I first heard this term many years ago while serving in the Marine Corps. We used it on patrols to indicate where to look for potential danger, using the hands of a clock. Nine o’clock is to your left, three o’clock is to your right, and six o’clock or “six” is behind you. Most people understand this concept. It has grown and been used in varying forms ever since, such as “I’ve got your six” or “I’ve got your back”, etc.
It’s important to always watch your six or have a trusted friend or spouse to watch your back to help you move forward without worry of what is behind. You can only see in one direction at a time and move toward the direction you are looking. You are better off to have another to walk with you. You can watch each other’s six.
This explains why fellowship with other believers is so important. You are not meant to be alone and isolated. That is when you are most exposed and subject to attacks from all directions. When you are aligned with others you build a wall of protection through prayer and teaching of God’s Word. Guard your hearts and minds continually and don’t give a place for the enemy to enter your perimeter.
1 Corinthians 16:13 (NLT) - Be on guard. Stand firm in the faith. Be courageous. Be strong.