Can someone explain to me what makes someone a lukewarm christian? [Spirituality & Religion]

I read a lot about it but I don't fully understand it, because when do I know when I'm sinning or just overthinking? Or am I making excuses to myself? Like for example when I think of what I should wear, is it sinning? If I want to look decent but not over the top, is it sinning? Is sinning not that you worry about worldly problems? I bought myself some food today even though we have enough at home and then I felt like I learned nothing. Did you ever feel like you didn't fully commit?