But I don't even know what it means to serve money.
No, really, what on earth does that mean (Matthew 6:24)? Apparently I'm not the first to ask the question, and I think that this article gets at least this much right: it's a warning,
against the kind of storing up that is a symptom of greed and acquisitiveness, of the love of money, and a love of the independence from God that it seems to allow.
It means that we should “be content with [our] wages,” (Luke 3:14), and not oppress others in our pursuit of worldly gain (Proverbs 14:31).
But it doesn't mean that we completely quit our jobs and take up robbing banks (Ephesians 4:28) or live off charity (II Thessalonians 3:7-8). Certainly if we are called to formal ministry then we are to partake of the earthly fruit of our ministry for sustenance (I Corinthians 9:7), but we are not meant to simply live off the grace of others (II Thessalonians 3:10).
So, we walk an easy balance between making money for the sake of making money (and who cares who we step on), and not making enough money to care for ourselves and our household. But that's not all! It also means that we help out our brothers whenever we can (I John 3:17), and support both formal ministries and the less fortunate (Deuteronomy 14:29). We are stewards of God's money here on earth, so we're supposed to do with it as He wills.
None of that really speaks to what it means to be a servant to money. II Peter 2:19 is the heart of it: if you are overcome by money, you are slave to it… you're serving the wrong thing. So what is it to be overcome by money? When we look to money, and not God, for happiness, that's the wrong answer. When we seek material gain or focus on our careers to the exclusion of daily fellowship with God and our brothers, it's the wrong answer. When our families are well cared for but we let worry about the future convince us to hold back every dime (or even one dime) that might be better spent in good work, it's the wrong answer. It's being overcome - mastered and enslaved - by money.
Colossians 3:23-24 gives us the right idea: work for the Lord. We work to do the best job we can, as a testimony to Christ in us, not as a testimony to convince our bosses we should get promoted. We work to support ourselves for the work of Christ (Philippians 1:21), not to gain one more bauble or one more fifty inch flatscreen. I Timothy 6:8 is the attitude we need - if we have food to eat, clothes to wear, and maybe a roof over our heads and running water, what else do we really need?
There are plenty of frugality blogs out there that will ask you to examine everything you have in order to save money for the purpose of saving money. I think God is asking us to examine everything we have in order to save money for the purpose of serving God.