Concerning doubt and faith: One of the things that has helped me is to remember to be honest both with questions and with doubts (and they aren’t always the same, though sometimes they might be or they might be related), but to also be honest about the truth or faith that you do have (however inexplicable or even indefensible to others). We rarely have full certainty and light (and with some things it’s honest to say “I don’t know” or “I’m uncertain” though I’d like to believe or be more certain), but what we must do is to be true to the light we have, whatever degree of light that is. Being true to the light one has includes, but is not limited to, intellectual and personal honesty. It is more profoundly marked by a life of loving, faithful living in Christ, who is the Light.
It might be with that kind of understanding that the Lord’s admonition to “Doubt not” would make sense. At the very least, in all the doubt and uncertainty that may arise, Christ is asking us not to doubt him (which implies we have something of knowledge/light of and from him). Doubts may/will show up. He asks us not to have a doubtful heart. I don’t know all that he means by telling us not to have a doubtful heart, though that implies that what we do, how we approach things, can have an influence with some aspects of doubt. The wise counsel “Doubt your doubts before you doubt your beliefs” may be one way, though not the only way, of saying be true to the light you have and work to not have a doubtful heart, to not receive what God sends with a doubtful heart.