But stealing, sexual immorality, killing of another human are certainly sins.
Think about why you think these things are wrong.
Also think about the difference between sin and morally wrong.
Sin is about breaking commands in a religious system. Morality isn't about rules and regulations, but about considering effects and consequences of your behaviour.
Some things aren't listed as sins in your system of religious beliefs, yet you may consider them wrong anyway.
Other things may (historically) be listed as sins, but you don't consider them morally wrong per se (example: eating pork, mixing fibers in clothing).
I consider stealing and murder wrong for the effects these actions have on other humans, but not sins (as I don't subscribe to the concept of sin).