Change is all about measuring yourself against a standard, being dissatisfied with where you are because you see that you have fallen short of the standard, and seeking the grace to close the gap from where you are to where you need to be. James likened the Word of God to a mirror (James 1:22-25) into which we can look and see ourselves as we actually are.
It is impossible to overstate how important this is. Accurate diagnosis always precedes effective cure. You only know that the board is too short because you can place it against a measuring instrument. You only know that the temperature in your house is too hot because you have a measuring instrument in your house (called a thermostat). You only know that your tires have enough air because you can use a gauge that measures their exact air pressure. The Bible is God's ultimate measuring instrument. It is meant to function in each of our lives as a spiritual tape measure. We can place ourselves and our marriages next to it and see if we measure up to God's standard. God's Word is one of his sweetest gifts of grace, and open eyes to see it clearly and an open heart to receive it willingly are sure signs of God's grace.
Understand the concept of indwelling sin.
One of the most tempting fallacies for us—and for every human being in this fallen world—is to believe that our greatest problems exist outside us rather than inside us. It's easy to fall into thinking this way, because we have a lot of material to work with. We live in a broken world where things don't operate as intended. Every day is filled with difficulties and obstacles of some kind. We live with flawed people, and our lives will be complicated by their brokenness. Despite this, the Bible calls us to humbly confess that the greatest, deepest, most abiding problem each of us faces is inside, not outside, of us. The Bible names that problem—sin. Because sin is self-focused and self-serving, it is antisocial and destructive to our relationships. Here's where this goes: it requires each of us to say that our greatest marital problem exists inside us, not outside us.
You know that you have been gifted with grace when you are able to say, "My greatest marital problem is me." It is so easy to point the finger. It is so easy to blame. It is a blessing to acknowledge that you carry around in yourself your own personal Judas who will betray you again and again (see Romans 7), and it is comforting to know that you are not alone in your struggle with sin.