6 ideas
The Lamp of Sacrifice holds that a building gains moral worth when its makers give more precious material and labour than use requires. The offering counts because it costs something, not because it is useful. Ruskin favours spending on the best materials and most careful work over producing more buildings cheaply.
The Lamp of Truth names three dishonesties. Structural deceits suggest a way of carrying weight other than the real one. Surface deceits paint one material to look like another, such as graining wood or marbling plaster. Operative deceits pass off cast or machine-made ornament as handwork. Each is wrong because it lies about how the building was made or what it is made of.
Ruskin says the right question about any ornament is simply whether it was done with enjoyment. Under the Lamp of Life, the irregularities and roughness of hand-cut work show that a living, thinking person made it. Uniform mechanical precision shows that the maker's mind was absent.
Under the Lamp of Memory, Ruskin calls restoration a lie and the most total destruction a building can suffer. It replaces the original workmen's marks, and the accumulated evidence of age, with a modern copy. He argues for protecting and propping old buildings as they are and letting them die honestly rather than falsifying them.
Ruskin argues that decorating railway stations is absurd. Travellers there are hurried and anxious and cannot contemplate beauty, so the ornament is money thrown away. The principle behind the example comes from the Lamp of Beauty: ornament belongs where people can rest and look, and places of rush and work should be plain.
The Lamp of Obedience argues that a nation's architecture flourishes only when builders accept a single common style. Ruskin proposes adopting an existing Gothic idiom rather than chasing novelty or mixing styles. Originality then comes from mastery within the shared discipline, not from inventing new systems, in the same way that a common language enables expression rather than preventing it.