Rock-solid means: ‘not likely to change, fail, or collapse.’
You and I as Christians should have a rock-solid life, which means that we stand out in this life because of our faith and confidence in God and His Word, which project a certain behavior that differs from people who do not have a rock-solid foundation. When adversity, trials, circumstances, difficulties, hard times, and stressful situations arise, we act and behave differently because our lives are rock-solid.