I'll stick with the "theories" of the Church, not armchair theologians, mostly unschooled.

We are given a whole lifetime to use in order to draw closer in union with Jesus Christ...yes "to use".  To "use" the human struggle (struggling to love ever more perfectly - though it is against our easier grain) to come to know Him and love Him and be with Him.  

He gives us the dignity of this union.  He made it possible.

But so few - as He Himself told us - take the narrow gate.