what counts is the un recognising israel based on its borders during that time, each time the un recognises a country it does so within the borders they currently occupy, unless stated otherwise. when the us recognised china it explicitly stopped recognising taiwan as an independant state, so did the un.
did they recognize Israel's borders at the time? i don't know. Do you?
you give your own interpretation to the word "secure", but who says those weren't secure and who says they don't mean "certain", "stable", etc.
you must ascribe the interpretation to the term as it was meant to be applied at the time. Looking at the way in which this resolution was formulated and the behind the scenes discussions, it is clear that the word secure, coupled with the purposeful removal of the word ALL, resulted in a resolution which required Israel to withdraw to different, secure (unlike the previous borders, which were uniformly recognized to not be secure and defensible) borders.
says who? Israel only once almost lost a war, and it was in its current borders!