When grilling or smoking meats many times an injection recipe is used to add flavor and keep the inside of the meat moist. A rub will add flavor and create a bark on the outside of the meat but the meat will dry out if not treated for interior moisture.
In our spiritual lives we need to allow God to inject us. This allowance is from His word, our prayer life, and meditation on Him. All of these actions we take in pursuit of holiness. Let us remain focused on Him, studying the word and books written by Godly persons, and praying without ceasing.