He who dwells …shall abide cannot be talking about the same action.  Yashab is clearly resident, and lûn is definitely stay overnight.  The person who is currently using the divine hiding place –  the seter, סתר – as dwelling place or, frankly, home,  will [try to] make himself stay overnight.  It is obvious that the seter is not the usual residence: it is the place where one takes cover, or hides.  Perhaps “bunker” is another way to think of the secret place or shelter.  The shadow of El Shaddai is also both a substantial permanent cover and a temporary refuge.  Compare the wings of a bird as the place where fledglings find protection (Deuteronomy 32:11  and Matthew 23:37).  “Abide” seems to be unrealistic when both places are incidental locations of refuge.

“He who dwells in the shelter of the Most High Will abide in the shadow of the Almighty.”

Psalms 91:1

The temporary and permanent elements of “shadow” are evident

• A ROOF IS A SHADOW/ SHADE. “Now behold, I have two daughters who have not had relations with man; please let me bring them out to you, and do to them whatever you like; only do nothing to these men, inasmuch as they have come under the shelter of my roof.” (Genesis 19:8, NASB).  Lot had offered his house for an overnight stay, saying, “Now behold, my lords, please turn aside into your servant’s house, and SPEND THE NIGHT, and wash your feet; then you may rise early and go on your way.” They said however, “No, but we shall SPEND THE NIGHT in the square.” (Genesis 19:2, NASB)
• A TREE PROVIDES SHADE.  ‘All the birds of the heavens nested in its boughs, And under its branches all the beasts of the field gave birth, And all great nations lived under its shade.” (Ezekiel 31:6, NASB)
• WINGS PROVIDE SHADOW/SHELTER “How precious is Your lovingkindness, O God! And the children of men take refuge in the shadow of Your wings.” (Psalms 36:7, NASB)
• YAHWEH HIMSELF IS THE BELIEVER’S SHADE. The Lord is your keeper; The Lord is your shade on your right hand.” (Psalms 121:5, NASB)
• THE Divine SHADOW IS A SOURCE OF HOPE  “Those who live in his shadow Will again raise grain, And they will blossom like the vine. His renown will be like the wine of Lebanon.” (Hosea 14:7, NASB)

When I look into many of the popular sayings in the Bible I particularly like finding a reason to say “Hey, what’s going on here?” Well, this “dwelling” and “abiding” in Psalm 91 looks kind of fishy and at least your curiosity has to be aroused seeing synonyms like DWELL and ABIDE appearing in this song from the 10th century BC.  Neither dwell nor abide are 21st century usage.  Now it is clear that ABIDING for lûn could not be the intended meaning over against dwelling (yashab), because abiding is really the overnight experience rather than a daytime homey experience.  When strangers arrive in the daytime one offers them shelter, footcare and food (Genesis 18:1ff).  When strangers arrive in the nighttime one offers them shelter, footcare,  food and a sleepover (Genesis 19:1ff).  If DWELLING in Psalm 91 is residing then a sleepover – ABIDING –  is nothing.  The reflexive stem (hithpael) of the verb tells us that the person who experiences a daytime welcome and secretive hospitality will make himself a sleepover guest.

“HE WHO DWELLS in the shelter of the Most High WILL ABIDE in the shadow of the Almighty.”

Psalms 91:1

Walk right in, sit right down, sleep over if you wish

From a homey and sheltering welcome to a sleepover seems to be a better transition and a certified improvement over dwelling and abiding.