Matthew 28:17 And when they saw him, they worshipped him: but some doubted.
Mark 16:14 Afterward he appeared unto the eleven as they sat at meat, and upbraided them with their unbelief and hardness of heart, because they believed not them which had seen him after he was risen.
Luke 24:41 And while they yet believed not for joy, and wondered, he said unto them, Have ye here any meat?
I copy for you here from the synoptic gospels a common thread. Once we have entered into a new life, the ability to doubt, to fear and be anxious remains. In a new born child we see only what we want from our own perspective. None of us remember how we felt when we were first born.
Being born again, being this new creation, comes with memories, habits, tendencies, and external relationships which influence us much more than when life first began. It is only natural to wonder about this new life and just exactly what has changed. Doubt is natural but it is not spiritual.
Jesus in those earliest of days of the born again will try and dissuade doubt, fear and anxiety. My rebirth came to me later in life and I have some memory of those first few days. I cannot say I believed for joy as indicated in Luke 24:41. I was amazed, I know that. Perhaps it was a form of joy I couldn’t express. My transformation was almost instant. It was an obvious change, so sudden and unexpected, it was obvious to everyone who knew me.
The fear, doubt and anxiety I had to deal with in those days were those of my children. I think my wife was more accepting but doubt probably lingered waiting to see if this change was permanent. It was not only permanent, change continued as I grew in Christ.
She had not yet learned to trust the new me.