Of course, Jesus knows everything, and we needn’t explain anything to God. That’s not the point. God give us autonomy. We’re free to turn to him or not. If we wish to, or need to share our hearts with him, that’s what prayer is for. It’s communication, it’s sharing, it’s asking for help when we need it, it’s trusting God and engaging him in our lives.
Suppose you were faced with the task of lifting a 100-pound bag of cement, and you’re only 100 pounds yourself, and there’s no way you can lift that bag. But you NEED to lift it. Wouldn’t you ask a friend for help?
Same thing with prayer. You’re burdened with something you can’t handle on your own and you need help from someone far more capable than you are to handle the situation righteously. Of course, God knows all about your burden before you mention it to him – but he won’t interfere with your freedom. You need to ask him for help, and then you’re including him in the process.
Sometimes, we are so awed and inspired by the greatness of God, we just want to tell him so. That’s also prayer. A prayer of praise.
And, sometimes, we very sorry about something we’ve done and we need to express our regret and ask for forgiveness. That’s also prayer. And it’s another area in which we find we need help, and ask for it.
There are lots of reasons to pray. Telling God what he already knows isn’t an insult. It’s an honor, because we’re acknowledging his omnipotence, and giving him credit for it. And, sometimes, we need to clarify things in our own minds, and explaining our situation to God helps us with that.