The connector For indicates a logical relationship with the previous verse. It may be rendered “because.”

My angel is with you: My angel becomes “God’s angel” in Good News Translation to avoid an awkward shifting of persons. See also verse 3. For background to this verse, see Exo 23.23-24: “When my angel goes before you … you shall not bow down to their gods….” See also Exo 32.34. Angel is translated “God’s messenger” in a number of languages, so a possible rendering for the whole clause is “God’s messenger will be there with you.”

He is watching your lives may be rendered “he will take care of [or, help] you” (Good News Translation).

Quoted with permission from Bullard, Roger A. and Hatton, Howard A. A Handbook on The Shorter Books of the Deuterocanon. (UBS Helps for Translators). New York: UBS, 2006. For this and other handbooks for translators see here.