Why can't I speak Spanish in public?

I would say that I am to the point in studying Spanish where I am "semi-fluent." That is, I can read most things, I can write and speak tolerably well (i.e. with generally good grammar and I can say almost anything I need to say, although sometimes it takes a bit of thinking to phrase it). For example, I am fluent enough to translate services at my church, and most of the time I think I do an OK job. I can even understand a lot of what people say when I am watching TV. Not everything, and it depends on the subject matter and people, but a lot. Almost my entire Spanish study has been made by listening - to CDs, videos, etc.

So why is it that when I actually try to talk to somebody, I fail so miserably? Not so much in the speaking part, but in the understanding part. I know that I know most of the words and virtually all of the grammar they are using - but, nonetheless, when it comes to actually using Spanish to communicate bi-directionally with people, I fail miserably. Why is that?

I don't think that it's simply that they speak too fast. I can understand fairly rapid speech. Part of the problem is the people don't always speak clearly: they (we all do it) mumble. But the biggest problem, I think, is that I get nervous. I miss something, and then they are standing there waiting for me to respond, and I feel like a complete loser. I live in dread of them switching back to English because I can't hack it; which, of course, they usually do, because their conversational ability in English is almost always way better than mine is in Spanish.

This is on my mind because yesterday we went to a wonderful Bolivian/Argentinian restaurant for lunch. Most of the staff did not speak much English, but seeing that we were gringos I guess they sat us at one of the tables with an English-speaking waitress. So, as I usually do, I worked up the nerve to speak Spanish with her, which she was happy to do. We were doing ok, until I asked her some question, and I didn't understand her answer. Now, there I was in my worst situation: she's said something, expects me to respond, and I don't have a clue. I could ask her to repeat it, but I know from experience I seldom do better on the second time through. She finally gave up on me and repeated it in English.

The thing is, I learned Spanish in the first place because I believe that God has opened a door for me to minister to Latinos in the community. There are many more in recent years, and they need the Gospel as much as we do. What's more, there seems a dearth of solid Spanish sources of Biblical Christianity around. There are Pentacostals, prosperity preachers, Catholics, and now seeker-oriented churches that have ministries to Hispanics, but I don't know of any other solid Bible preaching in Spanish around us. So, if God has called me to it, why aren't I making better progress?

Now, don't get me wrong: I think my progress is pretty good. I have been studying Spanish in total on my own for less than three years. I think that's pretty good for having an understanding of almost the entire grammar and a pretty sizable vocab (I'd guess several thousand words). But I don't seem to be making any additional progress, especially as pertains conversation: honestly, I don't feel any more comfortable conversing with people in Spanish than I did after a year. And, if I can't converse with people, I feel like I am not very useful in helping them into God's kingdom.

It's a bit depressing sometimes. I guess I will keep practicing, keep translating, and hope something happens. Pray for me.