I used to be one of those naive Christians who thought that the Gospel is easy to believe. After a few years now of struggling to believe even the most simple declarations of the Gospel (i.e., that God's love isn't dependent on my performance), I realize that I require God's grace even to believe His grace. Charles Hodge (some guy Jerry Bridges quotes in The Discipline of Grace) says this much better:

"The great difficulty with many Christians is that they cannot persuade themselves that Christ (or God) loves them; and the reason why they cannot feel confident of the love of God, is, that they know they do not deserve his love, on the contrary, that they are in the highest degree unlovely. How can the infinitely pure God love those who are defiled with sin, who are proud, selfish, discontented, ungrateful, disobedient? This, indeed, is hard to believe."

Bridges continues, "This is why it is so important that we keep the Gospel before us every day. Because we sin every day, and our consciences condemn us every day, we need the Gospel every day" (123).

What's the big point here? This is the big point: You cannot rely on your feelings alone to convince you of God's love and favor toward you. You MUST rely on something independent of your fickle emotions...something wholly outside of your deceitful heart. What is this something? It is the breathed out Word of God. Just as the Spirit brings salvation through the Word, He also brings assurance of salvation through the Word. The way we "keep the Gospel before us every day" as Bridges exhorts is to seek the very face of our Father in His Word and in prayer. And guess what...even when you fail to read your Bible or pray, His loving kindness toward you is just as certain as it is during those days when your heart is on fire for Christ and you are in the Word constantly.