Mercury enters Sagittarius at 9:42 pm EST tomorrow promoting inspiration. It will not be the actual planet acting on you. It will be in how you act regarding Mercury’s symbolism and position. Begin with how Mercury’s symbolism, combined with the cycles and patterns of its real and apparent motion, manifest in your life.
Then extend to the role of awareness — your awareness — in determining the outcome. Awareness alone makes a big difference, but you can make an even bigger difference by how you act on it. Ultimately, how you build and act upon the awareness of Mercury’s ingress to Sagittarius will determine how you are inspired and what you inspire in others.
The actual planet Mercury orbits the Sun on the inside lane of the solar system. That fact alone confers both the symbolism of Mercury as mind and its appearance to inhabitants of Earth as the fastest moving planet.
When you consider that the actual Sun is most fundamentally day and light to inhabitants of Earth, it makes sense to interpret the Sun symbolically as the light of consciousness. Following from that, it also makes sense to interpret the closest planet to the Sun as your fast-moving mind.