The Lord is the everlasting God,
the Creator of the ends of the earth.
He does not faint or grow weary;
his understanding is unsearchable.
he gives power to the faint,
and strengthens the powerless. (Isaiah 40 28-29)
I've read various commentaries on this passage, and learned much. Westermann, Childs, Seitz, Goldingay, and Brueggemann's own commentary. But just to prove that the best comment on Scripture text isn't always found in commentaries, here's Brueggemann in his book with the disconcerting title Text under Negotiation. The Bible and Postmodern Imagination. (Minneapolis: Fortress, 1993) It is replete with theological insight expressed in pastorally alert terms, and earthed in text, church and world. My copy is split, and the loose pages make it more like a loose-leaf folder - but I don't want to buy another because this one is annotated. But it's still in print and it remains a significant and persuasive example of exegetical confidence in the capacities of biblical text to help us reconceive our world in the light of the Gospel. So here's his comment on that famous Isaiah 40 text, found on pages 35-6.
Evangelical concern may derivatively raise the issue of our terrible disorderedness that issues in unseemly anxiety and in inescapable fatigue. It is a good question to raise in a local parish; Why so driven, so insatiable, so restless? The answer, in this doxological tradition, is that our lives are driven because we are seriously at variance from God's gracious food-giving program.
And where there is a variance and a refusal to trust:
youth are faint and weary,
the young are exhausted,
and there is little liberated flying or exhilarated running. (Isaiah 40.30)