"We do not know what we ought to pray for, but the Spirit himself intercedes for us through wordless groans." — Romans 8:26
In Romans 8, the apostle Paul explains that believers have a weakness when it comes to prayer. This involves much more than simply neglecting prayer or praying with wrong motives. Our weakness runs much deeper.
The best way to understand it is to compare it to the work the Spirit does to help us. We need the Holy Spirit to pray on our behalf because "we do not know what we ought to pray for."
This does not mean we never know what to pray for. Many of us have long lists of valid prayer concerns. Our weakness, though, is that we do not understand how the things we pray for fit into the mysterious, sovereign will of God. It's best understood as a spiritual disability.
So, as Paul describes it, "the Spirit intercedes for God's people in accordance with the will of God." Though there is much we do not understand, the Spirit understands completely. The Spirit situates the weakness of our prayers within the strength of God's intentions. Our broken prayers are taken up and incorporated into divine purposes that we know nothing about.
We can trust the mystery of prayer! God is at work. As we pray, the Spirit is also praying. There is much we do not know, but we can know this: "that in all things God works for the good of those who love him."