Because, “All Scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness, that the man of God may be complete, thoroughly equipped for every good work.”
Why? 1 Peter tells us “that we have been given great and precious promises, that through these you may be partakers of the divine nature, having escaped the corruption that is in the world.”
Here we have the purpose, the power, and the plan for discovering what the mind of God is for His children in knowing Him. There is nothing that can still our hearts and mind, giving quiet confidence and drawing us into His presence as hiding the promises of God within our soul.
As a child of God, we want to grow up and become disciples (learners) that desire to sit at His feet and learn of Him. In memorizing the promises we can be pleasing to His heart and His Word brings life, comfort and hopes to us. Take some time to focus on the promises of God and in communion with Him, ask that they are made real in your life.