'Work of the Lord' in the Bible

So, then, my beloved brethren, - become ye, steadfast, immovable, superabounding in the work of the Lord, at all times; knowing that, your toil, is not in vain in the Lord.

But, if Timothy should come, see that, without fear, he be with you, for, in the work of the Lord, doth he labour, even as, I:

Because, for the sake of the work of the Lord, unto death, he drew nigh, running hazard with his life, that he might fill up your lack of the public service, towards me.