Where did the "humans become angels" tradition come from? I'm clear that according to scripture, humans don't become angels. I read through the question on the topic (What Bible verses suggest that humans can become angels?) and didn't find an answer to my question: 

Can anyone provide references to the reason that people began to believe that loved ones become angels? I'm trying to understand how this well-established tradition evolved in Western culture.
this might not truly answer your question. but it does shed some light about &quot;us&quot; becoming &quot;like&quot; angels.

Luke 12:25
For when they shall rise from the dead, they neither marry, nor are given in marriage--&quot;neither can they die any more&quot; ( Luke 20:36 ). Marriage is ordained to perpetuate the human family; but as there will be no breaches by death in the future state, this ordinance will cease.
but are as the angels which are in heaven--In Luke ( Luke 20:36 ) it is &quot;equal unto the angels.&quot; But as the subject is death and resurrection, we are not warranted to extend the equality here taught beyond the one point--the immortality of their nature. A beautiful clause is added in Luke ( Luke 20:36 )--&quot;and are the children of God&quot;--not in respect of character, which is not here spoken of, but of nature--&quot;being the children of the resurrection,&quot; as rising to an undecaying existence ( Romans 8:21 Romans 8:23 ), and so being the children of their Father's immortality ( 1 Timothy 6:16 ).

Bible Study Tools
I imagine that somewhere along the way that people saw this as they would become angels when they went to heaven.  this doesn't say that at all. it really means equal unto the angels
this may be where we started thinking that we too could become Angels. but we really shouldn't want that.  We as saved individuals will become physical/spiritual beings after the resurrection, the Angels are only spiritual beings.
I could not find much more information on the subject, I am at work so I am rather limited in my research time.