Martyn Lloyd-Jones, from Studies in The Sermon on the Mount (Kindle Edition):
How does one therefore become `poor in spirit’? The answer is that you do not look at yourself or begin by trying to do things to yourself. That was the whole error of monasticism. Those poor men in their desire to do this said, `I must go out of society, I must scarify my flesh and suffer hardship, I must mutilate my body.’ No, no, the more you do that the more conscious will you be of yourself, and the less `poor in spirit’. The way to become poor in spirit is to look at God. Read this Book about Him, read His law, look at what He expects from us, contemplate standing before Him. It is also to look at the Lord Jesus Christ and to view Him as we see Him in the Gospels. The more we do that the more we shall understand the reaction of the apostles when, looking at Him and something He had just done, they said, `Lord, increase our faith.’ Their faith, they felt, was nothing. They felt it was so weak and so poor. `Lord, increase our faith. We thought we had something because we had cast out devils and preached Thy word, but now we feel we have nothing; increase our faith.’ Look at Him; and the more we look at Him, the more hopeless shall we feel by ourselves, and in and of ourselves, and the more shall we become `poor in spirit’. Look at Him, keep looking at Him. Look at the saints, look at the men who have been most filled with the Spirit and used. But above all, look again at Him, and then you will have nothing to do to yourself. It will be done. You cannot truly look at Him without feeling your absolute poverty, and emptiness. Then you say to Him,
Nothing in my hand I bring, Simply to Thy cross I cling.
Empty, hopeless, naked, vile. But He is the all-sufficient One-
Yea, all I need, in Thee to find, 0 Lamb of God, I come.