Psalm 15:5 (NIV)
He who does these things will never be shaken.
To be solidly grounded in Christ, one must not only believe in Him but also obey Him. Christ is a savior to many, but not their Lord. It's essential that we not just call Him Lord but also obey Him. The Lord's requirements are not burdensome but quite simple. He only needs us to love Him and help our fellow human. He who does these things will never be shaken.