With regards to Paul calling the "cross" a "tree," I think the only 
reference to that (at least that I can remember, I don't have a concordance 
handy) is in Gal 3:13 where Paul is basically quoting Deut. 21:23.  The 
word used in Gal 3:13 is _xulou_ [or, _ksulou_, depending on your 
transliteration ;-)], and, having no LXX available here at work, I have no 
idea if that is a quote from the Greek OT or if Paul has translated the 
Hebrew into Greek.  At any rate, I cannot remember any other time that Paul 
refers to the "cross" as a "tree".  In fact, doesn't Paul speak more of 
Jesus being "crucified" or of his "death" than of the actual "cross?"  
(N.B.--"Crucified"= _staurow_, a root similar to the word _stauros_).  But, 
hey, that is a different rabbit to chase! :-)  Greg, since you posted the 
original question, maybe you can get me on the right track here.  Are you 
asking if Paul's quote of Deut had a "missionary" motivation?  Or are you 
asking if Paul had a theological agenda for using "tree" instead of 
"cross"?  I'm not sure what you are looking for here, but with reference to 
Gal 3:13, the simplest answer to your question would be that Paul used 
"tree" instead of "cross" because his source (i.e., Deut) used "tree" 
instead of "cross".  Are you asking more than that?

Leo Percer
Baylor University