China does not want — ever — for there to be an American client state on its border, and they are doing what they can to prop up Pyongyang, and visits like this may be intended to keep Pyongyang in line. Particularly since a Washington envoy (Stephen Bosworth) is coming a couple weeks after that.
The last thing Beijing wants is for Pyongyang to make some unexpected deal that loosens their grip on the DPRK. Things like, say, declaring all of Shinŭiju a hermetically sealed free-trade zone with a Chinese-born Dutch governor. Things like that.
Anyway, enough of my opinions; this is what the BBC had to say:
China has been a firm ally of the North since they fought together in the Korean War against the South.No force on earth? Not even hunger or a sense that you're going to die anyway if you do nothing?
Analysts have noted, however, that China appears increasingly willing to push the boundaries of its special relationship with the North to support the nuclear talks.
China fears a huge influx of refugees if the North Korean state collapse, and has little desire to see a nuclear-armed state with an uncertain political succession on its border.
Mr Liang told a reception by Pyongyang's defence chief Kim Yong-chun that the bilateral relationship was "sealed in blood" when he and other Chinese troops fought the Korean War on the North Koreans' side.
"No force on earth can break the unity of the armies and peoples of the two countries and it will last forever," Mr Liang said, according to KCNA, the North Korean news agency.
"It is the fixed stand of the Korean army and people to invariably consolidate and develop the DPRK (North Korea)-China friendship, which has stood all trials of history," Kim Yong-Chun said.
The defence chiefs then had "comradely and friendly" talks, according to the report.