It is possible for human beings to ascend from one level to a higher one, but it is a task involving great exertion.
In fact, our spiritual personas can be likened to a multistory building where the first, lowest floor in the building is the nefesh level, above it is the ruah level, and above that is the neshama level.
Above that is the lofty level of the soul called hayya, and above this is the ultimate level called yehida.
All of these levels exist within everyone.
However, some of them are accessed only by certain individuals.
Most of us dwell on the ground floor of this multistory building, the nefesh level, and do not necessarily occupy that floor fully.
We start to ascend when our awareness of our inner selves does not remain at the first level but starts to rise.
While success in making this ascension is due, in some measure, to the grace of God or our God-given gifts, it depends first and foremost on our own conscious decision to attempt the climb.
But even if most people choose to remain on the ground floor – and there are those who actually prefer the basement – the entire building is open to anyone who makes the effort.
–Rabbi Adin Steinsaltz