There is a principle at work her in the spiritual life that applies to all of life, whether memorizing scripture, exercise, diets, paying debt, learning a foreign language, etc.
It's the secret to why some people fail at these things, while others succeed.
Here it is: I tend to overestimate how much I can accomplish in a short time, but I tend to underestimate how much I can accomplish by consistent habits over a long time.
For example, I think I can never in a million years memorize Paul's letter to the Philippians. Well, maybe not a million years, but how about in six months? Yes, I know a man who was able to memorize the entire letter to the Philippians in six months. How did he do it? He just listened to it on his mp3 player every day as he went walking, and he added a few verses each day. By continuing to repeat it, he memorized the entire book of the Bible!
Many people go on a diet for a week, and when they don't see results, they give up. They overestimate what can happen in a short time. But in a long time, much can happen. Last fall, I joined the YMCA and bought a bicycle to ride to the YMCA and then work out. By regular exercise on the treadmill and lifting weights five and six days a week, I have lost 22 pounds and I have also gotten stronger and can pick up heavier weights. The first week I didn't see much change, but over time...
Another example, is paying debt. My wife and I have paid off several credit cards but consistently paying the same amount, and when the minimum payment required goes down, we continue to pay just as much as we did the previous month. Also, we quit charging. By doing this, we paid off two credit cards, and we will soon pay off two more. We are still a work in progress, but in time...

So what goals do you have in your life? How does God want to work in your life? Stick with it! Don't give up, and over time, you will see what can happen!