Actually, I really like what Rick Warren had to say on the topic of what Paul meant by “working out your salvation”: He said (paraphrasing) that when we “work out,” we don’t work out to get a body, we work out to develop our bodies. In the same fashion, Paul is telling us not to “work out” to get salvation, but to “work out” to develop it.”
And also, when asked what the greatest commandment was, that’s when Jesus summed up the 10 Commandments into two: “Love the Lord your God with all your heart, with all your mind, and with all your strength. This is the first and greatest commandment.” That’s when He summed up the first four commandments. “The second is like it. Love your neighbor as yourself.” That summed up the last six commandments.