Doubt is an evil sin that should be repented of. It is not something to seek.
“Without faith it is IMPOSSIBLE to please God.”
I don’t think he’s talking about seeking it.
However, I think that he’s encouraging people to be honest with themselves about it. That everyone confronts it at some point in their lives.
There have been times when I’ve taken a step back and evaluated what I believe. I’ve had doubts about my salvation in the past. Several things have happened over the years that have removed that doubt, but still, especially for the new Christian, I don’t think it’s uncommon at all to have doubts.
But if they aren’t addressed, they will never be resolved.