Is it a Sin?

In a world where sin gets only a sneer from many, I recently had an interesting discussion about sin. The discussion was interesting in terms of sins large and small, and the question of whether we've lowered the morality bar so far that we might think we're morally clean, when we're really not.

Let's assume we're honestly trying to be good people. We successfully avoid the big ones - we don't murder, steal, covet, have sex outside marriage, etc. But how do we handle the smaller things?

For example,

Is it sinful to work in the yard on Sunday? To work for a retail shop that's open on Sunday? If the shop sells alcohol? To patronize stores on Sunday?

If it's stealing to take office supplies home from your employer for personal use, is it sinful if you happen to have a pen from the office in your pocket and use it at home just because it's handy?

Suppose you're in a shop looking for something specific, but the shop is out of stock. An employee at the shop hands you a partially used and open packet of what you want, telling you, "No charge, just take it". Suppose the value of what you were given at the shop was less than a dollar. Are you stealing from the shop?

Suppose you make a purchase in a store, and some time after you think the store clerk may have made a mistake and given you more change than you were due. If you don't immediately go back to the store to return the change, are you a thief?

If you don't tithe (give 10% of your income to God's work), is it a sin? If you do tithe, but grumble about it every time you write the check, is it a sin? If you give your money to worthy Christian causes but shut off funding to your own church because you disagree with something there, are you sinning?

If you voice your disagreement in your church over what you believe is improper behavior by the church's leadership, are you guilty of fomenting disunity and harming the congregation?

If you buy an expensive car, a vacation home, a boat, etc., is it sinful to indulge yourself when the money could have been spent doing God's work? Can it be fairly said that it's sinful simply to desire such luxuries?

If you hand cash to a panhandler on the street, knowing it will be used for alcohol or drugs, are you mistreating the panhandler? If you pass by and do nothing, is it better or worse than handing over the cash?

Is it a sin to do consulting and training for casinos? To work for one full-time?

Even if you are innocent, it it a sin to spend a lot of time with people who are currently, actively, and unapologetically living a sinful lifestyle?

If someone asks you to lie to another, even if it's meant to protect the other from the truth, should you lie, tell the truth, or keep silent?

You can probably make up your own list. The fundamental question boils down to, how can someone sincerely trying to live a good life and set a good example do so in a culture that despises good?