It means, that changing one of those variables may, as well as may not, lead to changing the other. We can not apriori say which is how much likely.
Imagine, that you can force somebody to increase the knowledge about science. If evidence is correlational it may or may not result in changing the trust. If there existed causal evidence, that knowledge causes trust, it is highly likely, that interventionally changing (for example by motivating to learn) knowledge of a person will have the effect of changing the trust.
Also the other way. Imagine, that you can change somebody's trust. If evidence is correlational, changing somebody's trust to science, may, or may not, result in gaining knowledge. Causal evidence make such effect much more likely.
The reasons for such distinctions are many.
One of them is that correlation do not distinguish direction. There is possibility, that only knowledge causes trust, but not the other way. Also, there is possibility, that first people gain trust, then knowledge. Also, there is possibility, that the relation is bicausal: when someone gains some knowledge, gains some trust, but trust then motivates to gain even more knowledge, which leads to even higher rust.
The other is, that maybe such relation do not exist directly, but it is caused by third variable. For example studying in college. If person goes to college such person both gain knowledge, and is persuaded, that science make sense, because meets a lot of people, who trust science, and make a living of it. Unless we make special analysis, which may take such things into consideration, we do not know for sure if causal relation exists at all.
The third example is that maybe people, which are analysed, and such correlational evidence is derived are selected in a way, that "makes" correlation without any relation between them. For example if we make such analysis on the group of people, who are successful scientist, assuming, that success requires both knowledge and trust in what they are doing, such correlation may appear, but changing one of the variables will not result in any reaction from the other.