Why Jeremiah 10:5 was changed from palm trees to scarecrows So, I was interested in reading Jeremiah 10:1-5 as it referred to Christmas trees. I found the comparison is very striking in the King James Version. As I was looking into this, however, I noticed that some other bible translations compared the tree to a scarecrows in a cucumber field, which I found very odd. 

When and why was this changed?

My other question is in regards to the first sentence of Jer 10:5. I get the first part, "They are upright as the palm tree, but speak not:", but I don't understand the second part "they must needs be born because they cannot go". What does this mean and how does it relate to a palm tree?
I generally agree with another answer and comments that “modern translations are better”, but I will elaborate a bit on how the variant translations came about. The Hebrew of interest:


  כְּתֹ֨מֶר מִקְשָׁ֥ה הֵ֙מָּה֙
  kətōmer miqšâ hēmmâ
  They [the idols] are like a tōmer of a miqšâ


Both tōmer and miqšâ are somewhat obscure. Tōmer appears only here in the OT. The KJV assumed an emendation to tāmār = palm tree (occurs 12 times in the OT), supported by the Vulgate: palmae. The Greek Septuagint doesn’t include this statement at all, so it’s not helpful. However, it is a Greek text that pushed translators in the direction of “scarecrow”. From the Epistle of Jeremiah 69(70):1 


  Ὥσπερ γὰρ ἐν σικυηράτῳ προβασκάνιον οὐδὲν φυλάσσον, οὕτως οἱ θεοὶ αὐτῶν εἰσιν ξύλινοι καὶ περίχρυσοι καὶ περιάργυροι.
  Like a scarecrow in a cucumber bed that guards nothing, so are their gods of wood, overlaid with gold and silver.


Προβασκάνιον (probaskanion) is a reasonably well-attested word for "scarecrow". This secures the meaning of tōmer in Jer 10:5 because it coheres with the context: the other term there, miqšâ, means cucumber field.2 


  If the object stands in a cucumber field, it has to be a scarecrow.3 


Consistent with the sense of the verse, Lundbom goes on to cite evidence from classical writers about statues of gods being used as scarecrows.

As to your second question, the KJV actually says, 


  they must needs be borne4  because they can not go


There’s no reason to work with the meaning “palm tree” at this point, but whether it’s a palm tree or a scarecrow, the point is that they are inanimate and therefore lame; they must be carried (“borne”).  

Summary
The KJV translators were uncertain the meaning of tōmer in the Masoretic text, so they accepted an emendation of the vocalization toward the reading of the Vulgate, arriving at "palm tree". In light of external evidence, translators now nearly universally accept that the meaning is "scarecrow".




1. Deuterocanonical for Roman Catholics and Orthodox; Apocryphal for Protestants. The earliest manuscripts, from Qumran, and are in Greek. The letter is a harangue against idols that is loosely based on the book of (proto)canonical 
Jeremiah.
  


2. See also Isaiah 1:8, where the KJV agrees. The Greek is σικυήρατον in both Is 1:8 (LXX) and Ep Jer 70(69), from σίκυς (sikus) = cucumber.
 


3. Jack R. Lundbom, Jeremiah 1-20. (The Anchor Yale Bible; New Haven: Yale University Press, 1974), 586.
  


4. Not born as in the question. To be borne is the passive form of a somewhat archaic use of the verb “to bear” meaning “to support the weight of”. The Hebrew term is often glossed “to be carried”.