There isn't one single "biggest" sin in Judaism, but idolatry, murder, and certain sexual sins (like incest) are considered cardinal transgressions that one must not commit, even if it means death, under the principle of ye'hareg v'al ya'avor ("be killed but do not transgress"). However, sins between people (like dishonesty) can sometimes be seen as worse than those between a person and God if they corrupt the whole community, and many traditions emphasize love for one's neighbor as a great principle, making interpersonal sins highly significant.
There's no single #1 worst sin; it depends on the religious or moral framework, but pride is often called the root of all evil (Christianity/Islam), while the blasphemy against the Holy Spirit (unforgivable sin) is considered the gravest in the Bible. Other severe sins include child abuse (Catholicism) and sins that "cry to Heaven" (like shedding innocent blood or oppressing the poor).
All of us are engaged in a personal, ongoing battle with sin and vice. The seven deadly sins--lust, greed, envy, anger, pride, gluttony, and sloth--are our main antagonists in this struggle.
There isn't a universal list, but many faiths identify core transgressions, with common contenders for "biggest sins" including pride, idolatry, murder, sexual immorality, and denying the Holy Ghost, often seen as the source or most severe violations, stemming from putting self or other gods before the divine.
Biblical prohibitions
In the Hebrew Bible, sexual relationships between siblings are forbidden to Jews but permissible to Gentiles (non-Jews). The relationships forbidden by Leviticus 18 are: One's genetic relative (Leviticus 18:6) One's mother (Leviticus 18:7) One's father (Leviticus 18:7)
In Judaism one is not only permitted but required to perform most sins, if necessary in order to save human life. This principle is called pikuach nefesh. The only exceptions are the three exceptional sins (murder, idolatry, and sexual misconduct), which one must die rather than commit.
However, Maimonides said that there are three commandments that should never be violated: 1) worship of other gods, 2) forbidden sexual relations, and 3) murder. Maimonides said that there are steps a person must take in order to repent from their sin. First, they must recognize that what they did is a sin.
The unpardonable sin is blasphemy against the Holy Spirit. Blasphemy includes ridicule and attributing the works of the Holy Spirit to the devil.
Those guilty of committing the unpardonable sin of denying the Holy Ghost and the unforgivable sin of shedding innocent blood must face the justice of God.
And, at any time, we are obligated to allow ourselves to be killed rather than transgress one of the three cardinal sins—idolatry, murder, and certain forbidden sexual relations (such as adultery, incest, and homosexuality).
The 10 Rules of Judaism are the Ten Commandments (Aseret ha-Dibrot), given by God to Moses at Mount Sinai, outlining fundamental ethical and religious duties, including worshipping one God, honoring parents, keeping the Sabbath holy, and prohibitions against murder, adultery, stealing, lying, and idolatry. They serve as core laws guiding Jewish life, emphasizing a covenant between God and the Jewish people.
Forgiveness can only be accepted from the victim. Judaism places great emphasis on teshuva. It is a way of atoning and requires cessation of the harmful act, regret over the action, confession and then repentance. Yom Kippur is the Day of Atonement, when Jews particularly strive to perform teshuva., or repentance.
Cain was their first son, and Abel their second. The majority of Biblical interpreters—throughout the ages—have considered Adam and Eve's disobedient act of eating the forbidden fruit (Genesis 3:6) as the first sin in the Bible—the moment sin and death entered the world.
In truth the Bible lists three unforgivable sins, which contradicts what Jesus said about the subject they are as follows:
No one is too far gone. No one has out-sinned Jesus's willingness to forgive. The only thing more powerful than our sin is the life-giving, sin-cleansing grace of God. There is no sin too big.
Pride is known as hubris (from the Ancient Greek ὕβρις) or futility; it is considered the original and worst of the seven deadly sins—the most demonic—on almost every list. Pride is also thought to be the source of the other capital sins. Pride is viewed as the opposite of humility.
I want to assure you that for all those in Christ, the answer to this question is a resounding "Yes!" Yes, God will forgive all of your sins. Even the ones that have plagued you the longest and consumed you the most.
Original sin is a Christian concept that states that all people are born sinful because humans' earliest ancestors disobeyed God. The story of this disobedience is included in the book of Genesis in the Christian Bible.
If we were to be asked what is the most severe transgression in the Torah, we would likely answer one of the three cardinal sins for which one must give up his or her life, if necessary, so as not to commit them: murder, idol worship and engaging in certain forbidden relationships.
Evil or profane speaking of God. The essence of the crime consists in the impious purpose in using the words, and does not necessarily include the performance of any desecrating act.
In contrast to Christianity, Judaism holds that we are neither born with sin, nor do we place responsibility for our sin within the realm of divine forces. To be clear, there is no concept of original sin in Jewish theology. As with Adam and Eve, God creates us as innocent human beings.