I think we may be talking past each other a little, so I’ll try to clarify the specific points you raised.
I’m not claiming the Bible contains a single, modern-style sentence that says, “Here is the technical definition of sin.” The Bible consistently explains sin in the same way it explains many of its key concepts — through story, teaching, contrast and consequence. It does this for love, justice, wisdom and faith as well. That isn’t evasive; it’s simply how ancient texts work.
For example, Scripture repeatedly shows sin as relational rupture rather than just rule-breaking: Genesis 3 portrays sin as a breakdown of trust and relationship with God. Isaiah 59:2 explicitly says, “your iniquities have separated you from your God.” Psalm 51 describes sin as something that corrupts the heart and requires restoration. romans 1-3 presents sin as humanity turning away from God, resulting in disorder and brokenness.
That’s why Christians often use “sin” as shorthand for what damages or fractures relationship with God — just as betrayal damages a marriage or selfishness damages a friendship. You don’t need a dictionary definition to recognise when a relationship is broken.
On Jesus and the law: Christians don’t believe Jesus “cancelled” the Mosaic law or declared it meaningless. He says he came to fulfil it (Matthew 5:17). Fulfilment means bringing it to its intended goal and revealing its deeper purpose. That’s why Jesus repeatedly relocates sin from external observance to the heart: Matthew 5 anger as the root of murder, lust as the root of adultery. Mark 7:15–23 is very explicit on this and says what defiles a person comes from the heart, not from food. Matthew 23 sets out a condemnation of meticulous law-keeping without mercy, justice or love.
Jesus doesn’t give a single soundbite saying “pork is now permitted.” Instead, he reframes defilement entirely. The early church later recognises the implications of this explicitly in Acts 10 and Acts 15.
On Mosaic law more broadly (including difficult issues like slavery), Christians don’t believe it functioned as a timeless moral code for all cultures. Even within the Bible it’s treated as covenant-specific and provisional (Galatians 3–4; Hebrews). Jesus’ ethic of neighbour-love and human dignity undermines practices like slavery rather than endorsing it.
Pulling isolated verses apart in debate can make it hard to understand the faith. If you are searching, I’d suggest exploring more with someone in person. It’s a narrative faith that’s meant to be read as a whole, often in conversation with others. That’s why many people find it more helpful to explore these questions through a church reading group, Christianity Explored, or Alpha — spaces where you can go deeper, ask hard questions, and understand the intentions and claims being made.
You don’t have to agree with Christianity — but this is the framework Christians are operating within, and it’s internally coherent even if you ultimately reject its premises.