Be Steadfast, immovable, what does that mean?

I was reading and ran across a verse that told me to be steadfast, immovable, always abounding in the work of the Lord, knowing that my toil is not in vain in the Lord.

My question is, what is the work of the Lord for me?

Why did God chose me and appoint me to bear fruit?

What did He see in me, that I have not seen in myself!

What is this that Christ laid hold of me for?

What is the prize of the upward call of God in Christ Jesus?

So many questions, who has the answer.

Doug