China is communicating loudly to India and to other members of P5 powers that its patience with India won't last forever, and that it will forcibly expel Indian troops from Doklam if India doesn't withdraw unilaterally:
Because Doklam is extremely close to India's vulnerable "Chicken Neck", the Siliguri corridor, this matter is vital to India's security. Likewise, because of its sensitivity, India has tens of thousands of troops near there, as compared to China's thousands. But because of that local asymmetry, China would likely resort to incursions on other parts of the border with India in order to make the whole border an active front.
PS: If they're going to attack, they'd better do it before the onset of winter forces a retreat.