The recording is missing the first part which is just the first 3 verses of Psalm 40. 1. The Psalmist (David) has waited patiently for the Lord previously and has been lifted out of the pit of destruction and had his feet put upon a rock (despite being back in the pit of destruction again - see v12). 2. The purpose of God lifting the Psalmist out of the pit (miry bog) is for his own glory first and foremost and so that other will see and believe as a result of this testimony. 3. The offer was put to the congregation to give testimony of a time this had happened to them.