CH02::mining: clarify what security miners provide re: valid txes

ch02.asciidoc

@@ -529,12 +529,14 @@ computation to verify as correct.
 The mining process serves two purposes in bitcoin:
 
 * ((("mining and consensus", "consensus rules", "security provided
-by")))((("consensus", see="mining and consensus")))Mining nodes validate
-all transactions by reference to bitcoin's _consensus rules_. Therefore,
-mining provides security for bitcoin transactions by rejecting invalid
-or malformed transactions.
-
-* Mining creates new bitcoin in each block, almost like a central bank
+by")))((("consensus", see="mining and consensus")))Miners can only
+receive honest income from creating blocks that follow all of Bitcoin's
+_consensus rules_.  Therefore, miners are normally incentivized to
+only include valid transactions in their blocks and the blocks they
+build upon.  This allows users to optionally trust that any transaction
+in a block is a valid transaction.
+
+* Mining currently creates new bitcoin in each block, almost like a central bank
 printing new money. The amount of bitcoin created per block is limited
 and diminishes with time, following a fixed issuance schedule.