The value of a continuous density function at a given point is also called its likelihood. Yes, the probability of getting any specific number in the range is exactly equal to 0—there are uncountably many options. However, it remains true that observations may cluster, and some values are still more likely than others.
For example, the probability that a standard normal variable $Z$ takes on the value $0$ is exactly the same that it takes on the value $1\times 10^8$, namely 0. But you will see $0$s much more often. This is reflected in the value of the pdf at the point, as any interval containing 0 is going to have a larger area, and thus larger probability, than any equal-length interval not containing 0 (the normal is symmetric and unimodal at 0).
So, informally speaking, the value of 0.4 is not useful for its magnitude in and of itself (although it is very useful in maximum and relative likelihood analyis), but it can be compared with other values on the curve to see which values may be more likely. But, as said earlier, probability only has positive value for intervals of continuous distributions.