We see in verse 4, God’s purpose for directing the apostle John to write these words. God wants His children to know the fulness of joy. It is not possible to know God’s joy unless a person knows the true God. God directed John to write about true fellowship. True fellowship is also only found in knowing the true God. Knowing the true God involves knowing the Lord Jesus Christ as well. A person cannot split up the Godhead and claim to have fellowship with God. A person cannot deny the deity of the Lord Jesus Christ and know the fullness of joy. Joy is not founded in our circumstances. Joy is founded upon knowing the forgiveness of sin that is found in knowing the true God and in having fellowship with the true God.
Based on the foundational truths found in verses 1-4, John was directed to give the key point of Jesus’ message to them while He was on this earth. Jesus had many things to say. All of them were important. Obviously we cannot distill all that Jesus said into the few words given here and expect to know all that God wants us to know.
What John was directed to tell us is that if we do not accept God as light, which includes the absence of darkness, we cannot fellowship with Him. We cannot accept anything else that God says if we do not accept Him as light. True light exposes darkness. When we know the true God, we will be able to understand what is going on in our world. The reason our governments are able to deceive so many people is because the people do not know the true God. Ungodly people are extremely gullible.
In our world we have a variety of types of lights. We have fluorescent tubes that give light. We have the spiral fluorescent lights. We have the standard candescent lights that have been around for a long time. There are also LED lights of many types. Then there are also candles and an assortment of flashlights. All of the lights that man has made leave shadows. If you are not close enough to those lights there will be a shadow. You will not see everything clearly. However, when we talk of God, He is light and there is no darkness at all. When we know the true God and walk with Him, we will see things clearly.
Verse 6 tells us that if we say we have fellowship with Him and walk in darkness, we lie and do not the truth. God’s Word is very clear on many things. Salvation is the central need of man. Since the fall of man, that is what man has needed, even though man did not recognize that need. All of humanity has been in darkness from birth since the fall of man.
We have stated before that salvation makes a huge difference in the heart and life of every born again Christian. Since the rise of New Evangelicalism, the clarity has been further muddied. God knows of the many attempts that Satan has made to twist the truth. Many people have accepted an “easy-believism” type of salvation that allows them to continue to walk in darkness and still claim to be saved. Many people are left scratching their heads as they observe what is commonly called Christianity, but it does not look any different than those who do not claim to be saved. It is not difficult to build a rather large following when we ignore what God says about salvation.
Some might argue and say that we all have our skeletons in the closet. They might also suggest that most people cannot even keep the skeleton in the closet. It is true that no born again Christian is without sin. John will address that fact in this chapter and in this book. The Nazarenes and the Apostolic groups claim that a person can arrive at a “higher” level of spirituality where they do not sin any longer. They still do things that are sin, but they re-classify them so that they are not sin any longer.
We notice in this book that God does not make a list of things that are sin. The danger then would be that a person might assume that he or she can check off that list and be good. In chapter 3 John wrote:

I John 3:4 Whosoever committeth sin transgresseth also the law: for sin is the transgression of the law.

God has no room for the piety that is common among us as people. God does not want anyone to think they are without sin. That is not reality for us on this earth. We do not become little gods when we are saved. We become “sons of God” when we are saved.

John 1:12 But as many as received him, to them gave he power to become the sons of God, even to them that believe on his name:
13 Which were born, not of blood, nor of the will of the flesh, nor of the will of man, but of God.

We are given the power to say no to sin and yes to God when we are saved.
We see in verse six that God does not accept the lie of claiming to have fellowship with God and walking in darkness. God tells us that to do this is a lie. I understand that a person cannot accuse another person of lying in the Parliament building any longer. The speaker will stop the person and demand an apology from them if they use that word. All of the politicians play along with that game and so the majority of the time lying goes on in that place without any checks and balances.
That is the world and we can expect lying to take place there. However, Christians have been saved. The blood of Jesus Christ has been applied to their hearts and they have been given a new nature. What God shows us here and elsewhere, is that true Christians cannot live in sin.
In verse 7 God began with the little word “but”. When the child of God walks in the light as Jesus Christ is in the light, then we have fellowship one with another. There is no substitute for true fellowship. Christians need that fellowship. In fact all people long for that fellowship in their soul. Most have seared their consciences to the place where they accept lying as a norm. However, in their soul they still know they are lying. It is important to be able to trust another person in what they say and do.
John tells us in verse 7 that the blood of Jesus Christ the Son of God, cleanseth us from all sin. That is what happens when a person is saved. That is also what happens when a child of God is walking in the light. It is possible to walk in the light. God shows us that we do not always do that, but it is possible to do that. God has provided the means for us to walk in the light. As a saved person walks humbly with the Lord, he or she will grow in the Lord and will have more times of walking in the light. However, the old man is always there and it is a fact that every true child of God will yield to the old man at times.

Psalm 119:104 Through thy precepts I get understanding: therefore I hate every false way.

Psalm 119:128 Therefore I esteem all thy precepts concerning all things to be right; and I hate every false way.