To be poor in spirit is:
It is to be satisfactorily poor and willing to be emptied of worldly wealth, if God orders that to be our lot. Many are poor in the world, but high in spirit, proud, murmuring and complaining and blaming their lot, but we must accommodate ourselves to our poverty, must know how to be abased. We must acknowledge the wisdom of God in appointing us to poverty, we must be easy in it, patiently bear the inconveniences of it, be thankful for what we have and make the best of that which is. It is to loose to all worldly wealth and not set our hearts upon it, but cheerfully to bear losses and disappointments which may befal us in the most prosperous state. It is not, in pride or pretence, to make ourselves poor, by throwing away what God has given us, but if we be rich in the world we must be poor in spirit, that is, we must sympathize for the poor and move with them, as being touched with the feeling of their infirmities.
We must expect and prepare for poverty; must not fear or avoid it, but must gladly welcome it, especially when it comes upon us for keeping a good conscience. It is to be humble and lowly in our own eyes. It is to think meanly of ourselves, of what we are, and have, and do. It is to be as little children in our opinion of ourselves, weak, foolish and insignificant. It is to value others and undervalue ourselves in comparison of them. It is to be willing to make ourselves cheap, and mean, and little, to do good; It is to become all things to all men. It is to acknowledge that God is great, and we are mean; that he is holy and we are sinful; that he is all and we are nothing, less than nothing, worse than nothing; and to humble ourselves before him, and under his mighty hand. It is to come off from all confidence in our own righteousness and strength, that we may depend only upon the merit of Christ for our justification, and the spirit and grace of Christ for our sanctification. That broken and contrite spirit with which the publican cried for mercy to a poor sinner, is that poverty of spirit. We must call ourselves poor, because always in want of God's grace, always begging at God's door, always hanging on in his house.
These are the one(who are mentioned above) who would enter into the kingdom of heaven. Only these are the one who fit to be members of Christ's church and the kingdom of glory is prepared for them. Those who thus humble themselves and comply with God when he humbles them, shall be thus exalted into the kingdom of heaven.