"Blessed are the poor in spirit, for theirs is the kingdom of heaven." (Matthew 5:3).
Amplified Bible:
Blessed (happy, to be envied, and spiritually prosperous-with life-joy and satisfaction in God's favor and salvation, regardless of their outward conditions)
are the poor in spirit (the humble, who rate themselves insignificant)
for theirs is the kingdom of heaven!
I want to make a very quick two points. The first point is that Jesus structured the Beatitudes in kind of a "triage" or "worst to best" order, so the "poor in spirit" are those who Jesus first addresses since theirs is the greatest poverty and pain.
Spirit does not mean religion. Spirit means much the way we would use the term nowadays. Spirit means having self esteem, zest for life, receiving the support, love and admiration that one is due, and having the life energy to thrive that comes from one's "spirit."
Notice that Jesus did not say: "Blessed are the poor in spirit because there are self-help books written by gurus who are oh, so spiritual themselves and who can teach you to be spiritual."
Jesus promised those who are poor in spirit, who feel downtrodden and who feel empty through no fault of their own, that they will have a total fullness of spirit in heaven.
In this way Jesus is also teaching that it is only from heaven that true "spirit" can be achieved. This is in contrast to people today who think they can "become" spiritual in this life. Having a richness of spirit is not the same as being an expert in the occult, or self hypnotising about one's own airy-fairy greatness. The most spiritual people are those who live good pious lives and who understand the source of their spirit is heaven and God, not from books, candles, crystals, looking smart to others and "detachment" exercises.
A lot of people miss this point of this first, most important, Beatitude, skipping over it thinking, "Oh, I'm very spiritual. I'm glad those poor other people who aren't spiritual will feel comforted when they die." Uh, uh, that is not what Jesus is saying at all. Jesus is teaching the source of true spirit in addition to assuring those who have a great emptiness and desire for spirit will be satisfied if they look to heaven and God. The greater the emptiness the more it can be filled (to fullness because they actually 'have' heaven) with authentic spirit from and in heaven. In a way Jesus is saying that the poorest in spirit on earth "inherit heaven," which is the total fullness of spirit from God in his presence.