At an early age, I remember asking my mom a deep, theological question: Why do we pray? After all, if God knows everything (including what you're about to ask Him), then why pray? My mom gave a very simple but true answer, "Well, I suppose it's because He wants us to talk to Him!"
Precisely. God knows every answer to every prayer you'll ever pray, but that doesn't take away from His desire for fellowship with you. He loves you, made you, and wants to spend time with you. Not only does it bring the Lord joy to commune with His children, but it helps us out in a number of ways.
What exactly do we accomplish by having daily devotions?
1. We're putting our armor on. Imagine being thrust into battle, exactly as you are at this moment. No gun, no helmet, no bulletproof vest, no boots... just everyday clothes. It's just as ridiculous to send a soldier into battle without his armor as it is for you to face temptations from the world, Satan, and you're own flesh without help from the Most High.
2. We're sharpening our ax. Imagine trying to cut down a huge tree with a dull ax. It would be much easier to accomplish your task if you stopped for five minutes and sharpened your tool. How often do we attempt to hack away at life without preparing ourselves through prayer? It's amazing how much smoother a day will go after asking God for strength.
3. We're plugging into the Power Source. I want to assign a science experiment to each of you. Try to make a lamp work without plugging it in. What? You mean it can't do it in its' own strength? John 15:5 says that without the Lord, we can do nothing. What makes us think we can accomplish everything we have planned this semester in our own strength? We must plug into the Power Source, because we are insufficient in of ourselves.
Also note Matthew 19:26, which states that with God, all things are possible!
without Him = nothing
with Him = anything
The difference is whether we choose to plug into God's power, or just decide that we can handle it on our own. Cultivating a relationship with the Lord not only makes Him happy; we greatly benefit from it, as well!