It seems to me that people learn a song for different reasons - nice tune, good plot, nice poetry, even a few good lines....
I have learned songs for specific reasons - feature evenings or theatrical performances for instance.
All these reasons will produce a reasonable performance, (providing you put in the work of course) but I don't believe any of them are enough to encourage you keep singing a song - I've found that a song you don't "feel for" will last as long as your original motivation wears so thin that you become bored with it - it ceases to surprise you.
I have not long started to sing again after a gap of 20-odd years and am finding it interesting to learn which of my largish repertoire I can just re-learn and which I have to totally re-think.
We started to record elderly traditional singers in 1973 and continued for thirty years,. We made a point of questioning as many as we could on what the songs meant to them, how they saw them, where they fitted into their lives, what they "saw" while they were singing them...... Without exception, everyone we asked talked about involvement, mental pictures, and above all "truth" and "belief".
Listen to singers like Sam Larner or Texas Gladden talking and you'll find a total committment to their songs.
If I was asked to choose between a skilful singer who could deliver his/her song perfectly and knew exactly where to put their fingers and when (assuming they sang accompanied), and one who is maybe past his/her prime, but was capable of communicating their feelings for their song - no competition - give me the latter every time - anything else is one-dimensional.
Jim Carroll