Here’s what I take ‘poor in Spirit’ to mean, but I’m not infallible:
Someone who is poor in spirit realizes that he is unable to provide for himself spiritually. He depends completely on God for his salvation. He knows that all of the good works he can scounge up will not be nearly enough to pay his debts. He trusts in God alone.
“Blessed are the poor in spirit for theirs is the kingdom of heaven.”