I listened a little while ago to a talk from John Piper entitled "Whatever is Not From Faith is Sin".
The title is a reference to Romans 14:23, which reads like this in the ESV:
For whatever does not proceed from faith is sin.
This passage comes out of the context of Paul talking about what is allowable to eat (bearing in mind that the majority of the very early Church to whom Paul was writing was Jewish, and had lived most their lives under strict food laws). Paul declares that no food is unclean in and of itself (Romans 14:14), but then points out that that fact is effectively irrelevant.
The complementary doctrine is that, just as much as no food is unclean in and of itself, everything is sin unless it stems from faith. In other words, it doesn't matter if what you're eating, or what you're doing is not unclean (or sinful) in and of itself, what matters is whether your heart is directed towards God.
Piper says:
The most penetrating and devastating definition of sin that I am aware of in Scripture is the last part of Romans 14:23: "Whatever is not from faith is sin." The reason it is penetrating is that it goes to the root of all sinful actions and attitudes, namely, the failure to trust God. And the reason it is devastating is that it sweeps away all our lists of dos and don'ts and makes anything, from preaching to house-painting, a candidate for sin... Anything, absolutely any act or attitude which is owing to a lack of trust in God is sin, no matter how moral it may appear to men. God looks on the heart.
This was the mistake of the Pharisees (Luke 11:42) - focusing on a list of "good actions" and a list of "bad actions", and utterly failing to love God. Everything they did then, came out of a desire to do everything on the good list, and avoid everything on the bad list; and so somehow make themselves sufficiently pleasing to God so that he might free their nation from Roman rule. The problem? It would never, ever work:
And without faith it is impossible to please God (Hebrews 11:6)
The mistake of the Pharisees is a mistake I own, time and time again. I want to honour God in the small things, and in the attempt, I make honouring God about the small things. Jesus said about this:
"Woe to you, teachers of the law and Pharisees, you hypocrites! You give a tenth of your spices—mint, dill and cumin. But you have neglected the more important matters of the law—justice, mercy and faithfulness. (Matthew 23:23)
This week I want to remember first to love God, and follow God out of a love for Him. Anything less is faithless, and whatever is not from faith is sin.