What is the meaning of "shield him with Your invincible support" and what is meant by "support" and "invincible"?

The meaning of the supplication "You have sought refuge in Your mighty pillar": You have sought by Your might, Your strength, and Your greatness, which no one can oppose. For the pillar (rukn) is the strong side, and Allah Almighty is the strongest and most impregnable of pillars.