Before Cain killed Abel, God recognized the hatred in his his heart, and in love God reached out to him to call him to repentance and restoration. God said to Cain: "If you do well, will you not be accepted? And if you do not do well, sin lies at the door. And its desire is for you, but you should rule over it" (Genesis 4:7). A cheap, easy religion masquerading as Christianity is making itself at home here in western culture. Its adherents take the doctrine of grace and avoid the rest of the Bible like the plague. How can such a belief square with scriptures like Deuteronomy 18:13, where the Lord commands us to "be blameless?" Now the usual response is something along the lines of "Well, that was the Old Testament." And in doing so, they dismiss more than half of the Bible, the Word of God. The real question should be, "Does the Lord intend for us in the New Testament to be blameless?" To answer that question, we need to understand the purpose of that command. Otherwise, we are nothing more than those who try to cast off God's restraints and live lawlessly.
Let's first look to Daniel to demonstrate the need for the child of God to live blamelessly, in verses 3-4 of chapter 6. When the jealous governors and satraps of Babylon sought to find fault with Daniel in order to bring charges against him, so that he would lose favor with Nebuchadnezzar, they could find nothing. In fact, the Bible says that "they could find no charge or fault, because he was faithful; nor was there any error or fault found in him." And we know that Daniel's faithfulness, along with that of Shadrach, Meshach, and Abednego, left Nebuchadnezzar no choice but to acknowledge the one God. And gentlemen, that is the reason why we must be blameless. Daniel didn't honor the Lord's commands out of some legalistic belief that he would be saved because of his own works. He was obedient so that he could have a relationship with God and the world around him would be able to see God through him.
Throughout the Bible light often symbolizes the Word of God, truth, and His guidance. In Micah 3 we see what happens when God's people are disobedient, and do not live blamelessly. Verse 6 reads: "Therefore you shall have night without vision, and you shall have darkness without divination; the sun shall go down on the prophets, and the day shall be dark for them." If we regard iniquity in our hearts, the Lord will not hear when we seek His direction (Psalm 66:18). Gabriel told Daniel in Daniel 9:23 that "at the beginning of [his] supplications the command went out..." We can see a contrast here between Daniel and the disobedient prophets from Micah 3. For Daniel, as soon as he began to pray God answered, but for the disobedient, only darkness.
For the naysayers who still reject the Lord's command for us to be blameless as an Old Testament relic, Jesus repeated the command in Matthew 5:48-6:2, when He said, "you are to be perfect, as your heavenly Father is perfect." (For further explanation read Romans 6:1-14, 7:5-8:8, 13:11-14; Galatians 5:13-17; 1 Corinthians 15:34; Ephesians 4:17-5:18; 1 Thessalonians 3:13-4:8, 5:4-8; 1 John 3:4.)
As Daniel was, we are called to be a priesthood before the Lord, a light by which the dying world may see God and put their faith in Him, just as we do (Exodus 19:5, 1 Peter 2:9).
"My little children, I am writing these things to you so that you may not sin. And if anyone sins, we have an Advocate with the Father, Jesus Christ the righteous..." (1 John 2:1)