Why is there not much we can do about our own weakness?
There is not much we can do about our own weakness because the struggle is in the invisible realm of the Spirit, not something we can handle by human effort. The Holy Spirit indwells believers and helps their infirmities, so the proper response is to let God do it.
Les teaches in this section that the Holy Spirit, who now indwells us according to Paul's teaching, also helps our infirmities, our weaknesses. He explains that there is not much we can do about it because we are dealing with the invisible and the realm of the Spirit. Therefore the instruction is, "But let God do it."
Likewise the Spirit also helpeth our infirmities: for we know not what we should pray for as we ought: but the Spirit itself maketh intercession for us with groanings which cannot be uttered.
More Questions
Does the Holy Spirit help us with our weaknesses?
The Holy Spirit, who now indwells believers, also helps them in their weaknesses.