In The Chrysalids, in Chapter 2, how are David and the others' secret connected to the sayings on the wall of the Storm's house?
The signs you refer to actually appear in Chapter 2, and not just in the kitchen, but in the big room in the Storm's house. Note how important these "truths" are to this community, that such signs are displayed in the key living areas. This is how David describes his house:
The nearest approach to decoration was a number of wooden panels with sayings, mostly from Repentances, artistically burnt into them. The one of the left of the fireplace read: ONLY THE IMAGE OF GOD IS MAN. The one on the right: KEEP PURE THE STOCK OF THE LORD. On the opposite wall two more said: BLESSED IS THE NORM, and IN PURITY OUR SALVATION. The largest was the one on the back wall, hung to face the door which led to the yard. It reminded everyone who came in: WATCH THOU FOR THE MUTANT!
David goes on to comment that even before he could read these statements were engraved on his memory - in fact, they might even have been used to teach him how to read. It shows how his community were so fanatical on preserving the "stock of the Lord" and how much they feared any form of mutation or difference.
Of course, it is key to note that this description comes after David's discovery of Sophie and her "deformity". The end of Chapter 1 narrates David's difficulties in understanding the "law" of his world as expressed through these signs, and ends with his questioning the value of such an approach. Of course, David as yet does not identify himself as a "Mutant", for he and the others do not have any visible signs of mutation, but eventually, when their secret is discovered, they are labelled as a new form of mutant, and all the more dangerous because of it.