"I have no motivation."
Maybe the idea of spending your free time working on missions doesn't appeal to you now. If you begin to pray about it and to learn what God is already doing to spread the Gospel to every nation, tongue and tribe around the world, God will give you a passion for mission work. It will become something you enjoy. It will make your life feel more meaningful. It will be a blessing to you and to others.
"What difference can I make?"
You might think, "How can I really make much difference working in missions from home or locally, in my spare time?" If missions were strictly a human endeavor, you'd be right. But Jesus is the one who gave us the Great Commission. It's a work that He's doing, through us, and it will be accomplished (Rev 7:9). So remember, that it's all-powerful God, working through you, that can accomplish much. And it's not just through you--it's through millions of followers of Jesus, world-wide, who are called to missions. You are one, important part of the body of Christ.
"I'm struggling with sin."
If you're struggling with some sin, don't let that keep you from participating in the Great Commission. Once you start giving, praying, going, serving regularly or mobilizing others, you will experience a change of heart. God will help you surrender that part of your life to Him, and He will replace it with something wonderful.