There are only two ways of salvation: by the law or by grace. If salvation is to happen by the law, perfect obedience is necessary. There can be no blemishes or shortcomings, for the law will never show mercy. It knows nothing of grace or forgiveness. It demands perfection, because whoever transgresses in one tiny detail transgresses the whole of God's law: "For whoever keeps the whole law but fails in one point has become accountable for all of it" (James 2:10). Getting to heaven through obedience to the law requires perfection. Merely doing your best will prove insufficient; good intentions are not enough. It is vitally important to grasp exactly how much the law demands if we think we are going to be in a right relationship with God through law-keeping. Simply put, "By works of the law no one will be justified" (Gal. 2:16).
This excerpt is taken from How the Gospel Brings Us All the Way Home by Derek Thomas.