1. What is sin according to the Bible?

Everyone who practices sin practices lawlessness as well. Indeed, sin is lawlessness. – 1 John 3:4

And if a soul sin, and hear the voice of swearing, and is a witness, whether he has seen or known of it; if he do not utter it, then he shall bear his iniquity. – Leviticus 5:1

An high look, and a proud heart, and the plowing of the wicked, is sin. – Proverbs 21:4

2. What is the origin of sin?

How you have fallen from heaven, O morning star, son of the dawn! You have been cut down to the ground, O destroyer of nations. You said in your heart: “I will ascend to the heavens; I will raise my throne above the stars of God. I will sit on the mount of assembly, in the far reaches of the north. I will ascend above the tops of the clouds; I will make myself like the Most High.” But you will be brought down to Sheol to the far reaches of the Pit. – Isaiah 14:12-15

Therefore, just as sin entered the world through one man, and death through sin, so also death was passed on to all men, because all sinned. – Romans 5:12

3. Why do we still constantly commit sin after we are forgiven of sin? What are the consequences?

I know that nothing good lives in me, that is, in my flesh; for I have the desire to do what is good, but I cannot carry it out. For I do not do the good I want to do. Instead, I keep on doing the evil I do not want to do. – Romans 7:18-19

Jesus replied, “Truly, truly, I tell you, everyone who sins is a slave to sin. A slave is not a permanent member of the family, but a son belongs to it forever. – John 8:34-35

Having eyes full of adultery, and that cannot cease from sin; beguiling unstable souls: an heart they have exercised with covetous practices; cursed children. – 2 Peter 2:14

The soul that sins, it shall die. The son shall not bear the iniquity of the father, neither shall the father bear the iniquity of the son: the righteousness of the righteous shall be on him, and the wickedness of the wicked shall be on him. – Ezekiel 18:20

For the wages of sin is death. – Romans 6:23

For if we sin willfully after that we have received the knowledge of the truth, there remains no more sacrifice for sins, But a certain fearful looking for of judgment and fiery indignation, which shall devour the adversaries. – Hebrews 10:26–27

But the fearful, and unbelieving, and the abominable, and murderers, and fornicators, and sorcerers, and idolaters, and all liars, shall have their part in the lake which burns with fire and brimstone: which is the second death. – Revelation 21:8

4. How can we escape sin and be purified?

“I have yet many things to say to you, but you cannot bear them now. However, when He, the Spirit of truth, is come, He will guide you into all truth: for He shall not speak of Himself; but whatever He shall hear, that shall He speak: and He will show you things to come”. – John 16:12–13

Sanctify them by the truth; Your word is truth. – John 17:17

“For the time is come that judgment must begin at the house of God”. – 1 Peter 4:17

He who rejects Me and does not receive My sayings, has one who judges him; the word I spoke is what will judge him at the last day. – John 12:47-48

“For the Father judges no man, but has committed all judgment to the Son”. – John 5:22

And it shall come to pass, that in all the land, said the LORD, two parts therein shall be cut off and die; but the third shall be left therein. And I will bring the third part through the fire, and will refine them as silver is refined, and will try them as gold is tried: they shall call on my name, and I will hear them: I will say, It is my people: and they shall say, The LORD is my God. – Zechariah 13:8-9