You frustrate the grace of God when you try to earn what has been freely given, when you think that you must do more for God to bless you, or that you must pay the price for it. The Almighty God desires that you know the things that have been freely given to you. He wants you to receive them freely although it cost Him His Son, but He wants you to receive the blessings freely. Just like the prodigal son, who deserved nothing, but received everything. God wants you to receive freely. He cannot give it to you based on your works because if it is by works, it is no longer by grace. When you try to work for it, you frustrate the grace of God.