SP 118 - Sin is a mistake in choice, which is most often caused by stupidity. But it is also a fault, because stupidity is caused by negligence. Stupidity and negligence mutually condition each other and separate from Wisdom and Love - from GOD.
SP 160 - Mortal sin kills Me in the sanctuary of the soul of a person who has sinned. If he persists in sin, I am dead in his soul and his soul is dead. This is the state that was after My death on the Cross, because by crucifying Me in himself, he crucifies his soul.
SP 222 - Every human sin makes a breach in My Kingdom of Love. Beware and watch yourself so that you do not succumb to temptation at the moment of intensification of the trial, which lasts continuously - your entire earthly life.
Ask Mary, the angels and the saints in Heaven for protection, so that you build My Kingdom and do not harm it with your sins. Every sin is building the kingdom of Satan on earth and in the hearts of people, every hostility and unkindness as well.

SP 358 - Alice: What is my sin?
JESUS: Confidence in yourself, your reasons and opinions, because you accuse others more than yourself. Know, My child, that the main accuser is Satan and it is he who inspires in your mind the tendency to trace evil in others and often talk about it. And also bitterness in your heart and regret because of your own imperfection. The colors in which you see people depend on your heart. On the transparency of your heart, thanks to which My Love can penetrate outside and illuminate what you look at. A pure heart allows you to see the truth - both good and evil - through the prism of My Merciful Love (in yourself and others).
SP 393 - By sinning, you harm yourself and you only sadden Me, because I do not want you to be harmed. Your happiness is My joy.
SP 451 - Do not expect anything from yourself except a tendency to sin. Apart from Me, nothing is good for you, especially now in the time of Satan's darkness over the world. Satan is everywhere, and My Wounds are the only shelter - they open the gates of salvation.

SDD 64 - Alice: What is sin?
JESUS: Departure from Me.

Alice: Man remains alone?
JESUS: Man is never alone. If he is not with Me, he is with Satan, who attracts him more and more to himself and makes him dependent. Most often imperceptibly, so as not to scare him away.
SDD 159 - Sin is the result of disobedience. In order to be obedient to My instructions, one must practice and perfect oneself by obedience to people who are placed higher. Also by obedience to oneself in fulfilling the obligations undertaken.
SDD 180 - Notice, feel and know that we are one. This unity is the meaning of your existence. Nothing else will fulfill this meaning. Everything else is a substitute, pain and a mistake. It creates a tear - separation from Me. It is the harm you do to yourself. This is sin - if you do this harm to yourself consciously, rejecting unity with Me.
Sin is not harm done to GOD. It is harm, pain, death done to yourself. "Sin" committed with the body is only sin when it hurts your soul or someone else's. If you commit it unconsciously and it does not hurt anyone's soul, it is not sin, because it does not create evil.
Fulfilling My will protects you from sin - from doing evil to someone or yourself. Consciously doing evil to someone is always evil done to yourself. For someone, however, it can be good, as long as they are able to accept it with love - as I taught.

SDD 421 - Alice: It is necessary to break with every sin.
What is sin in my case?
JESUS: Negligence from which good does not result, and sometimes even evil.
Allowing unkind thoughts and feelings that Satan suggests, and instead of giving them to Me immediately and asking for help, you hold them in your heart and succumb to them.
Your heart should be like glass, through which everything is visible and nothing is hidden.
You should pass on to Me what comes to you from the world, and pass on to the world what you receive from Me - to people for their healing.
All negligence destroys transparency. Therefore, take care and constantly take care of the purity of your heart. Ask for help so that I may change the glass of your heart into a crystal that will reflect the light of My love and transmit its rays to everyone.

SDD 610 - Each person, although he is powerless, can offer Me his desire to be with Me and to cooperate, serving. Veronica could do so little, and yet she did so much. She only wiped My face, because she wanted to show people My pure Face, without the dirt with which they cover Me in themselves. Without the dirt of their sins, which cover My Face in them.
She alone among many showed the greatest love and courage. That is why My Face remained in her: in her hands and in her heart. I gave her Myself to be My witness.
Ask, what does My Face look like in you? I came into your souls and I am in them. What is My Face like there? Is it clean?
Or are there perhaps traces of blows, bruises, wounds, dirt, spit? Ask, let each one answer in his heart, how much courage and love he has in himself to show My Face to others.

SDD 850 - ...Your desire (of suffering) soothes the pain that others inflict on Me.