Faith in Christ. The only way to hold fast is to believe more and more. Get a larger acquaintance with Christ, with His person, work, and character. Every page of the gospel unfolds a new feature in His character, every line of the epistles discloses new depths of His work. Get more faith, and you will get a firmer hold.
Faith is like the root.
Many believe a little concerning Christ, one fact. Every new truth concerning Jesus is a new root struck downward. Believe more intensely. A root may be in a right direction, but, not striking deep, it is easily torn up. Pray for deep-rooted faith.