Another way that Tillich helps readers view their changing world is by making the distinction between science and faith. Increasingly, it is also becoming more difficult to separate the two. As Tillich states: "The distinction between the truth of faith and the truth of science leads to a warning, directed to theologians, not to use recent scientific discoveries to confirm the truth of faith. Microphysics has undercut some scientific hypotheses concerning the calculability of the universe." Rather trying to choose sides in a struggle between religion and science, where it is difficult to determine one right and one wrong contender, Tillich goes above and beyond the fray by using the terminology "truth of faith," rather than "truth of religion."

Lastly, Tillich's book is "a blessing," because it puts the word "humble" back into religion. Recently, religious groups have become too sure of themselves and their beliefs. They are quick to discard the beliefs of others and too readily to believe that their religion must be followed. Tillich puts the "doubt" into the equation. Tillich notes in his book that if faith is understood as belief that something is true doubt is not compatible with...

However, on the other hand, if faith is understood as being the ultimate concern, then doubt is a necessary element within it. It is the result of the risk of faith.
The doubt that is an aspect of faith is not a doubt regarding facts or conclusions. It is not similar to the doubt that is at the fundamentals of science.

The doubt that is part of every act of faith is not the doubt of methodology or skepticism. Nor is it the doubt of the skeptic. Instead it is the doubt of someone who is ultimately concerned about a concrete content. It is an existential doubt instead of the skeptical or methodological doubt. Simultaneously, the doubt that is implied in faith accepts this insecurity and takes it into itself as an act of courage. Here's the ultimate way that Tillich is relieving the concerns of numerous Christians as well as members of other religious groups, who are afraid that they are suffering from a loss of faith. That's OK concludes Tillich. Doubt, even serious doubt is confirmation that faith exists. It notes the serious nature of the concern and its unconditional character.

Reference:

Tillach, Paul. Dynamics of Faith. NY: Harper, 1957.