In economics, physical tools of this sort are capital goods. Money is often just plain called capital. In sociology, the equivalent "stuff" is often termed cultural capital or social capital. In military terms, assets serving this function are force multipliers (which is by far the more easily-understood version, I think).
Marriage is a tool, in this sense. It allows a couple to change the way that people in general and many legal institutions view and treat them, and even the way they view themselves and each other. Denying that tool to gay people is a denial of agency, a statement that "we don't think we should have to treat you like that". It also does preserve that tool in ways that are fairly subtle, but are real - making marriage more inclusive does change the utility of that tool. Whether "preserving the integrity of marriage as a tool" is at the root of most of objections, or just a handy cover story for bigotry, is a whole other topic, though. Divorce law changes have altered the utility of the tool far more significantly.
This blog is such a tool, too. It allows me to spout opinion and have it sit, neatly organised and available to readers. This extends my expressions of opinion across people and time, magnifying their effects. In theory, I could just phone all my readers up and rant at them - but the blog is much more effective.
The specific tools you use to express will as agency also matter, plainly, even if they're both capable of similar things. A blog does not do the same things that a billboard does, even though they both carry messages in the form of words. Ball peen hammers aren't sledgehammers. Civil unions aren't marriages. Work visas aren't citizenships.
This isn't purely a matter of forcefulness, though. Condensing this blog post into a billboard slogan would be pointless, for example; it wouldn't translate well. Different tools have differing levels of force, but each also carries a hefty bias - and that bias can be internalized. People that are well set up for joining protest marches may well feel utterly unable to get their ideas across, if the best tool is lobbying or the creation of a press outlet that the media can treat as credible; everything looks like a reason to march.
Understanding the tools available to us gives us more agency, and more precision in how we apply it. Understanding where tools are denied to others, or available with differing costs, tells us something about the society we share.