to say: to put something into words, whether spoken aloud or set down in writing
This is by far the most common verb for speech in the New Testament, and it is deliberately plain. Where some verbs point to the act of making sounds or the manner of speaking, this one points to the content: what was actually said. It is the word that introduces nearly every quotation in the Gospels, the standing formula before Jesus' own words ("truly I say to you"), and the verb that reports what the Scriptures or the prophets state.
Because it is so general, its exact shade comes almost entirely from context. It can report a flat statement, a command, a question, a claim, a confession, or an objection, and the same verb covers all of them. The reader learns the force of any given saying from the words it introduces, not from this verb.
Its written sense is the same act in a different medium. When the New Testament reports what Scripture, the Law, or a prophet "says," it treats the written text as still speaking, so the verb that means "to say" naturally also means "what stands written here states."