Yes, there is only one sin that breaks our relationship with God. But, aren't there lots and lots of sins that we commit? Yes, but there is only one sin that breaks our relationship with God and that sin is the sin that is at the root of all the others we commit.
Let's look at where sin began and it will become clear that there is only one sin that separates us from God. All the others are simply symptoms of that one sin.
Lucifer was created perfect and lived in a perfect environment with God in Heaven. What happened? What changed and brought about his downfall? What sin did he commit or wrong action did he do? Isaiah tells us what happened in Isaiah 14:12-14. "How art thou fallen from heaven, O Lucifer, son of the morning! how art thou cut down to the ground, which didst weaken the nations! For thou hast said in thine heart, I will ascend into heaven, I will exalt my throne above the stars of God: I will sit also upon the mount of the congregation, in the sides of the north: I will ascend above the heights of the clouds; I will be like the most High."
What was Lucifer's sin? Isaiah points out that it was something that happened in his heart or mind. His sin was in his thoughts and for quite a while no one but God was aware of what was going on in his heart. What was his sin? Which commandment did he break? The very first one. "Thou shalt have no other gods before me." Exodus 20:3. He wanted to be like God. He wanted to decide for himself what was right and what was wrong. He wanted to "like the most High".
What Lucifer essentially said was that God could go ahead and be God, he could have His rules and require whatever He wanted, but he (Lucifer) was going to follow his own rules, ignore God's, as it suited him, and answer only to himself. And in doing so he put himself above God. One has to have (or presume to have) a higher position of authority to actually ignore or change the laws of another authority.
So, we understand that Lucifer's sin was rebelling against God's authority, putting himself above God, or disrespecting God.
What was Eve's sin? Let's look at what happened when she fell. "Now the serpent was more subtle than any beast of the field which the LORD God had made. And he said unto the woman, Yea, hath God said, Ye shall not eat of every tree of the garden? And the woman said unto the serpent, We may eat of the fruit of the trees of the garden: but of the fruit of the tree which is in the midst of the garden, God hath said, Ye shall not eat of it, neither shall ye touch it, lest ye die. And the serpent said unto the woman, Ye shall not surely die: For God doth know that in the day ye eat thereof, then your eyes shall be opened, and ye shall be as gods, knowing good and evil. And when the woman saw that the tree was good for food, and that it was pleasant to the eyes, and a tree to be desired to make one wise, she took of the fruit thereof, and did eat, and gave also unto her husband with her; and he did eat. And the eyes of them both were opened, and they knew that they were naked; and they sewed fig leaves together, and made themselves aprons." Genesis 3:1-7. Lucifer (Satan), speaking through the serpent said, you won't surely die. He was putting his authority above God's and Eve fell for it. She decided that she also could put her authority above God's and choose to do whatever she wanted to in spite of what God had said, ignoring God's authority and will. She reasoned that the fruit had given the serpent powers that it didn't previously have, and believed that she'd also receive benefit, as he suggested.
Eve sinned by making herself her own god and rebelling against God. This is really the root sin. All the other sinful things we think, do and say grow out of this. All the other sins are simply a symptom of our rebellion against God and his authority, making ourselves our own god and in doing so, putting ourselves above God. None of the other sins will be in our lives if we are not in rebellion against God and His authority. Think about it. Every time we choose to sin what have we done? We have rebelled against God and put ourselves above Him, made ourselves our own god, saying, "I am going to do it my way!" In other words, the very first Commandment is a real hedge to keep us from sin when we see the importance and significance that it holds for us.
It is not the greatness of the act of disobedience that constitutes sin, but the fact of variance from God's expressed will in the least particular; for this shows that there is yet communion between the soul and sin. The heart is divided in its service. There is a virtual denial of God, a rebellion against the laws of His government.
No one has salvation, a saving relationship, while in rebellion against God. Anyone who tells you that you are in a saving relationship with God while in deliberate, known, ongoing sin is promoting the same lie that Satan told Eve --"Ye shall not surely die." Is Jesus your Savior and the Lord of your life? Is He the controlling power in your life? If not, you have made yourself your own god and are in rebellion against God. Satan becomes the controlling power in your life by default. The Ten Commandments exalt God and by them we may see if we are in rebellion or not. "But we know that the law is good, if a man use it lawfully; knowing this, that the law is not made for a righteous man, but for the lawless and disobedient, for the ungodly and for sinners, for unholy and profane..." 1 Timothy 1:8, 9.
2 Timothy 2:15