There does not seem to be anything very obscure in the text of this psalm; but its title puts us on our mettle, it cries out for us to knock on its door. However, ‘blessed is the man who hopes in him’ (Psalm 33. 9), as it says here; so let us all be hoping he will open up to us when we knock. After all, he wouldn't urge us to knock if he didn't want to open up to us when we do. If it sometimes happens that a man who was intending to keep the door shut for the night will get up and open it against his own inclinations, because he cannot stand the din of the door-knocker any longer (Luke 11. 8); surely we have every reason to hope that he who said ‘Knock and the door will be opened to you’ (Matt. 7. 7), will open it promptly.