What should I tell them?

I find myself in the position of turning down an invitation to a dear friend's bridal shower in order to attend a "Leadership Development Day" with my church community. I don't think my "non-believing" friends even begin to comprehend why I would choose that over a "party." But my church community is my family. What we have goes deeper than friendship. What we have is _eternal_. I don't know how to explain that to them in a way that wouldn't somehow offend them. I'm particularly sensitive to that because before I had a relationship with Christ, I was easily offended (or at the least, turned off) by anything that I perceived as someone trying to "shove their beliefs down my throat." As a result, I'm horrible about sharing my faith. Unless someone asks a direct question, I barely talk about it. I know that, as followers of Christ, we are called to “Go out and make disciples of all nations” (Matthew 28:19), but I find that I can't get past my fear of alienating people. My hope is that people, especially friends & family who knew me before I came to Christ, will see the changes in me and realize that it's His hand on my life that has made this difference, and that they will want to know Him, having seen Him in me. But then I look at how I behave, day to day--my irritability, my petty judgements--and I think, "How can anyone see Jesus working in my life when I fall so very short of who I should be?"

This song expresses much of what I feel:

Shaun Groves "Should I Tell Them"
 
Walking with you is not without hazards
Tripping's this traveler's curse
Price paid for falling is more than my stumble
In a world that is watching and waiting for words
But I listened when You said to go
And I set out in spite of my fears
About truth mixed with my imperfection
And the question of what to say when I got here
And now that I'm here
Should I tell them that
You are the one who has made me
And saved me and set up a home there inside
Should I tell them that I am a perfect example
Of all You can do with a life.
What should I say to them?
What if I'm failing them?
What should I tell them tonight?
Now don't get me wrong
I'm thankful to be here
With this song to sing and a spotlight on me,
But lately I'm wondering if you are mistaken,
If you're seeing all of me there is to see.
'Cause on every face I detect
The same questions I've posed to you
Like do you speak through the imperfect
Are we too dirty for your light to get through?
I want your light to get through.
What should I tell them when
They're thirsty Lord
My cup is empty Lord
Come and lead me here in this place
Cuz I'm unashamed, but I'm unprepared
And I'm just plain afraid