Since we are beings experiencing life as our very own, doubt about spiritual realities such as eternal life, the loving kindness of God, or even that God exists, may sometimes arise. Swedenborg suggests that having such doubts is a normal and important part of our regeneration cycles.
There are two kinds of doubt: affirmative and negative. Affirmative doubt might be expressed something like this: "I don't understand this, but I would like to, and will try to live rightly and seek more understanding". Negative doubt might be more like, "I don't understand this, so I'm going to reject it."
In "A Guide for the Perplexed", by E.F. Schumacher, there's a scene right at the beginning of the book where the author is in Moscow on a tour of the city. He sees a beautiful church ahead of him. He consults his map, and it's not marked there. He consults his Soviet tour guide, who says that the church is not on the map because it's still an active church - not a monument or museum. Schumacher is struck by this -- and extends the thought to be that our maps of knowledge often leave out the important living unanswered questions.
(सन्दर्भ: Arcana Coelestia 4099, 5044 [1-13])