《宋书·志·卷十八》
进不凌犯至尊，退不威逼臣下，循考古今沿革，斟酌现在时宜，这样做很符合礼制。 
进不斥尊，退不逼下，沿古酌时，于礼为衷。 
Not overstepping the authority of the Emperor when going forward, and not oppressing subjects when going backward. This is in line with the ritual system, taking into account the changes from the past to the present and weighing the current needs.
<s>[INST] Kindly elucidate the central themes in this passage in English: 进不斥尊，退不逼下，沿古酌时，于礼为衷。  [/INST] Not overstepping the authority of the Emperor when going forward, and not oppressing subjects when going backward. This is in line with the ritual system, taking into account the changes from the past to the present and weighing the current needs.</s>
Kindly elucidate the central themes in this passage in English: 进不斥尊，退不逼下，沿古酌时，于礼为衷。
user
Not overstepping the authority of the Emperor when going forward, and not oppressing subjects when going backward. This is in line with the ritual system, taking into account the changes from the past to the present and weighing the current needs.
assistant