Mars in Libra is applying to a conjunction with Saturn. All the Mars/Libra scenarios that have been brewing since this transit began (see my original post here) will come to a head.
Saturn in Libra is about social consequences. How you experience the Mars/Saturn meeting will depend entirely on how you've been doing Mars in Libra. Careful, conscious use of this energy (starting something with another's needs in mind, balanced action, polite assertiveness) will net you solid results. You'll get a confirmation of something you desire (Mars). Alternatively, you could cross a threshold and finally complete something that's necessary (but not fun).
Careless use of this energy (passive agressive jabs, dithering, trampling over other people's boundaries) will get you payback. But not the nice kind. If you try to push a relationship or scenario further than it's supposed to go, you'll hit a wall. If you've been frittering away your energy, you'll be held accountable. The unpleasant side of Mars/Saturn is the authoritarian "No, you can't".
The action that's been taking place in the Libra occupied area of your chart will slow down as Mars approaches Saturn. It may feel like a grind, but it's Saturn's way of ensuring that you're on the right track. Do you really want this? Yes? Then it's worth the extra effort. So if things get sticky, dig in and push a little harder. Slow, concentrated efforts are the way to go (push too fast and you'll get burnt out). But... make sure you're pushing for something that's meant to happen. Re-read the 2nd and 3rd paragraphs of this post if you're not sure. The pace will pick up again after this aspect is exact (at 24 degrees Libra) on August 15th.
If you have planets between 17-24 degrees Libra you'll feel this most intensely.