Do you think it is plausible that David is basing his conviction in 1 Samuel 24:6, not to kill Saul, on Psalm 105:15? -- Reto Zingg

(For those who have not read 1 Samuel, please take a look before you read my response. Notice also a similar episode in 1 Samuel 26.)

Yes, I think so.This Psalm may well have been written long after the time of David, but it's certainly the same thought – that God protects and preserves his anointed ones. The passage in Psalms reads

12 When they were but few in number,
    few indeed, and strangers in it,
13 they wandered from nation to nation,
    from one kingdom to another.
14 He allowed no one to oppress them;
    for their sake he rebuked kings:
15 “Do not touch my anointed ones;
    do my prophets no harm.”

This passage refers to Abraham and those who follow him. Israel is not yet a nation ("...they were few in number...").

Samuel had anointed Saul, indicating God’s plan and favor. Of course by chapter 23 Samuel had also anointed David, leading to a high degree of tension, especially given Saul's jealous tendencies.

And yet we know that many prophets (and at least one priest) were killed. So…. this passage represents God’s will, even though it is not an absolute or predictive promise.

David's degree of respect for authority is an upward call to us all. We live in an era when the individual is exalted and authority is slandered. Even Christians' degree of disrespect for leadership is disheartening. Please see 1 Peter 2:11-17; Romans 13:1-7). We could all stand to learn a lesson from David, whose heart was (usually) in the right place!