The reason so many struggle with their faith is that they don’t know enough about God’s faithfulness to His Son. Our salvation is entirely in the hands of the Son of God our Savior and He is more than able to do more than we can ask or think. He has accomplished the full, complete, total and everlasting salvation of His people and nothing can ever change that.
Because these things are true, that it is in Him and by Him alone without anything from us, we can rest assured that even in the teeth of our faults, failings, desertions and rebellions, He never changes toward us. A believer has nothing to fear from God at all. Christ has fully taken away everything that would give God a reason to be angry with His people.
The Scriptures never tell us that we must have a certain amount of faith, that is religion, but that we must believe. Believe how much? The grain of a mustard seed. Small faith saves as well as great faith. It isn’t how much faith but simply faith.
Rest in Christ alone. Do not look to yourself for anything, especially feelings. Religion will point you to obedience (J. I. Packer, John MacArthur etc.) but obedience is never a gauge of faith but a result of it.
I am saved because the Great God and Savior the Lord Jesus Christ stood in my place and fully accomplished that which was required in my place. In Him I am complete, in Him I am accepted, in Him I am a son of God and that son-ship can never be severed. In Him I am blessed of God and all the glory of eternal bliss is already my by Him.
Even when I don’t feel like it.