For call those things hath mine hand made, and all those things have been, saith the Lord: But to this man will I look, even to him that is poor and of a contrite spirit, and trembleth at my word.
Isaiah 66:2 KJV
God is “looking,” he looking for a particular man or woman: one through whom he can speak, move, and bless. That person is a “humble” person, a person who knows that they cannot live life without Jesus. At its most basic, humility is seeing yourself as God sees you: dark yet lovely (Song of Songs 1:5), weak yet strong (2 Cor. 12:9), and poor yet spiritually rich (2 Cor. 5:21).
Humility is not thinking less of yourself, but thinking less about yourself. Humility is not denigrating yourself by making yourself out to be less than the total person that God has gifted and called you to be as his servant.
Having a, “contrite spirit,” is similar to maintaining an attitude of humility: a contrite spirit is a heart that is broken, needy, and yearning for help. It’s having a sense of sin: the emotional damage caused by sin, the selfishness that wounds others, and the helplessness that paralyzes. Contriteness is an awareness that our sin has hurt God and others, but it also acknowledges that God’s grace, mercy, and forgiveness is greater than our failure.
Last, “trembling” at God’s Word is an attitude of submission, openness, and obedience to God’s spoken and written word.
In all, a believer that God uses is humble, contrite of heart, and submitted to God’s Word: the same character qualities that Jesus describes as  “poor in spirit” in the Sermon on the Mount (Matt. 5:3). The “poor in spirit” acknowledges their complete and utter bankruptcy before God. Its admitting that we are spiritually, emotionally, and physically afflicted; completely unable to save ourselves.
In conclusion, the Lord is not looking for the adequate, successful, and influential: he seeks and supports those who know their need of him.
[God] has a heaven and earth of his own making, and a temple of man’s making; but he overlooks them all, that he may look with favour to him that is poor in spirit, humble and serious, self-abasing and self-denying, whose heart is truly contrite for sin, penitent for it, and in pain to get it pardoned, and who trembles at God’s word, not as Felix did, with a transient qualm that was over when the sermon was done, but with an habitual awe of God’s majesty and purity and an habitual dread of his justice and wrath. Such a heart is a living temple for God; he dwells there, and it is the place of his rest; it is like heaven and earth, his throne and his footstool.
Matthew Henry, Matthew Henry’s Commentary on the Whole Bible: Complete and Unabridged (Peabody: Hendrickson, 1996), Isa. 66:1–4.