- She was an idolator herself
- She was trying to prevent her father, Laban, from committing idolatry
Gen 31:19 doesn’t shed any light on this. It only states that she stole the idols.
But The Book of Jasher goes into detail.
40 And Rachel stole her father’s images, and she took them and she concealed them upon the camel upon which she sat, and she went on.
41 And this is the manner of the images; in taking a man who is the firstborn and slaying him and taking the hair off his head, and taking salt and salting the head and anointing it in oil, then taking a small tablet of copper or a tablet of gold and writing the name upon it, and placing the tablet under his tongue, and taking the head with the tablet under the tongue and putting it in the house, and lighting up lights before it and bowing down to it.
42 And at that time when they bow down to it, it speaks to them in all matters that they ask of it, through the power of the name which is written in it.
43 And some take in the figures of men, of gold and silver and go to them in times known to them, and the figures receive the influence of the stars, and tell them future things, and in this manner were the images which Rachel stole from her father.
44 And Rachel stole these images which were her father’s, in order that Laban might not know through them where Jacob had gone.
Wow! It was to protect Jacob. Not only does it tell you why, but how this particular idol operated! Kind of creepy!