Anything that throws more sand into the gears of western allies is to the benefit of a rival. Make people more afraid, make anything more expensive, more inconvenient, etc etc, until we throw our own countries into chaos.
Russia has been sowing division around the world, ie. hiring people to commit terror or antisemetic grafiti etc.
The point of this, is that divided societies are less strong, and more vulnerable to being influenced, so they have a higher success rate in promoting pro-russia far right parties.
Holding westerners hostage. The more they support Ukraine, the more terrorism westerners face. If they stop supporting Ukraine, the implication is that Russian terrorism would stop.