First Second and Third Persons

Psalms 91:9-10 KJV
Because thou hast made the LORD, which is my refuge, even the most High, thy habitation;
There shall no evil befall thee, neither shall any plague come nigh thy dwelling.

I see in this passage three persons;

First, there is the Lord
He is the object about which the Psalm is given.
He is the refuge
He is the Most High.
Later in the Psalm, the Lord becomes the speaker in through prophetic speech, but here He is the subject about which the speaker speaks.

Secondly, there is the Psalmist
While the penman is not now certainly known, many believe this was King David and I see little reason to question it.

And thirdly there is the reader/hearer
As this was a song, it would have been originally meant to be heard. The speaker or singer, whichever, makes this bold assertion;
"Because thou hast made the LORD, which is my refuge, even the most High, thy habitation;
There shall no evil befall thee, neither shall any plague come nigh thy dwelling."

I am reminded of Paul in the sinking ship telling the rest of the people on board, "fear not, for I believe God." Paul's faith, he believed, was sufficient for them all! The Psalmist says in very similar tones, "Because you have made the Lord, my refuge, your habitation, no evil shall befall thee."

This is the worker of the preacher and the Christian witness. We share our faith. We pass it out. We tell people what we know to be true from God's Word and as they place faith in it, God does for them what He has already done for us.