I had a difficult time reading the Diary of St. Faustina–it took me forever, and I only managed to get about 3/4 of the way through it. Then I lost interest, because it seemed so repetitive, and I found some of it hard to believe ( but I don’t doubt her in the least). I found her more difficult to read than St. Teresa of Avila, who is a difficult read. But I did get a greater appreciation of God’s Mercy, and I have always loved the Divine Mercy Chaplet.
I do not fully understand the Mystics, but I can appreciate their great love of God. I do not understand their degree of suffering, I do not desire to suffer like that, and I think that these people are truly blessed by God to be able to give of themselves to that degree. I also think that God has chosen them for this role before their birth–they seem to have a propensity for mysticism from early childhood, and a unique relationship with Him from early on.
I also think that if a person is not careful when they read them, they can begin to compare themselves with them, and get the impression that their own spirituality is somehow deficient. We can learn a great deal from them, but God relates to each one of us in a different way, and His gifts are given as He chooses, and are right for us in His Divine plan.
But, to get back to the topic, I can appreciate the difficulties in reading St. Faustina’s Diary, and I think the average Catholic would experience difficulty also. Don’t feel bad about it.