Do Not Forget Who is Writing
The primary question here is:
Can we infer from this, that sharing a meal together, at the time of
writing of this Psalm, indicate people who ate together had a much
greater depth of friendship?
An important point to remember is who is writing the Psalm. It is David, King of Israel. To share a table with a king indicated some "greater depth of friendship" than a casual acquaintance, for kings had to protect themselves more than the average person.
As to sharing a table, especially for David, it was an honor he bestowed specifically in one clear act of kindness for his deep friendship with Jonathan, by allowing Jonathan's one remaining son to eat bread at his table, so 2 Samuel chapter 9 (NKJV):
1 Now David said, “Is there still anyone who is left of the house of
Saul, that I may show him kindness for Jonathan’s sake?” 2 And there
was a servant of the house of Saul whose name was Ziba. So when they
had called him to David, the king said to him, “Are you Ziba?” He
said, “At your service!” 3 Then the king said, “Is there not still
someone of the house of Saul, to whom I may show the kindness of God?”
And Ziba said to the king, “There is still a son of Jonathan who is
lame in his feet.” 4 So the king said to him, “Where is he?” And Ziba
said to the king, “Indeed he is in the house of Machir the son of
Ammiel, in Lo Debar.” 5 Then King David sent and brought him out of
the house of Machir the son of Ammiel, from Lo Debar. 6 Now when
Mephibosheth the son of Jonathan, the son of Saul, had come to David,
he fell on his face and prostrated himself. Then David said,
“Mephibosheth?” And he answered, “Here is your servant!” 7 So David
said to him, “Do not fear, for I will surely show you kindness for
Jonathan your father’s sake, and will restore to you all the land of
Saul your grandfather; and you shall eat bread at my table
continually.” 8 Then he bowed himself, and said, “What is your
servant, that you should look upon such a dead dog as I?” 9 And the
king called to Ziba, Saul’s servant, and said to him, “I have given to
your master’s son all that belonged to Saul and to all his house.
10 You therefore, and your sons and your servants, shall work the land
for him, and you shall bring in the harvest, that your master’s son
may have food to eat. But Mephibosheth your master’s son shall eat
bread at my table always.” Now Ziba had fifteen sons and twenty
servants. 11 Then Ziba said to the king, “According to all that my
lord the king has commanded his servant, so will your servant do.” “As
for Mephibosheth,” said the king, “he shall eat at my table like one
of the king’s sons.” 12 Mephibosheth had a young son whose name was
Micha. And all who dwelt in the house of Ziba were servants of
Mephibosheth. 13 So Mephibosheth dwelt in Jerusalem, for he ate
continually at the king’s table. And he was lame in both his feet.
Ziba later calls into question the loyalty of Mephibosheth when David is fleeing Jerusalem in the wake of Absalom's take over (2 Sam 16:1-4), but Mephibosheth, upon David's return, states Ziba lied (2 Sam 19:24-30). While Scripture is not fully explicit on who is telling the truth or not between these two men, the statements of Mephibosheth appear strongly to favor his story, given that he states he does not care about having a part in the land, only the king's safe return (v.30). But amidst his statement he also conveys he understands the honor he had been given and the mercy David had shown (v.28):
"For all my father’s house were but dead men before my
lord the king. Yet you set your servant among those who eat at your
own table. Therefore what right have I still to cry out anymore to the
A place at King David's table was a special place. This does not mean that meals were only shared with close friends in the broader populace; but even broadly, one does not tend to eat with known enemies. This contrast to the one eating with David to also being his enemy is a contrast that likely would apply no matter who it was.
From commentators, there is one I am aware of that noticed this fact about the specialty of eating at a king's table. In A Commentary on the Holy Scriptures: Psalms, Carl Bernhard Moll around 1869-1870 noted it. It is part of the commentary series by John Peter Lange, later translated to English, edited, and further noted by a number of men: Philip Schaff, Charles A. Briggs, John Forsyth, James B. Hammond, J. Frederick McCurdy, and Thomas J. Conant. In that, it is written (emphasis added):
We are here to notice the sacredness of the rights of hospitality, the meaning of companionship at the table and the friendship of the guest among the ancients, especially in the Orient. It was a particular honor to eat at the king’s table (2 Sam. 9:10 sq.; 1 Kings 18:19; 2 Kings 25:29). There is no occasion to give up the very natural historical references and explain the expression typically of intimate intercourse (De Wette) or indeed of maintenance (Hupf.) and benefits in general.
So he specifically notes that there are some commentators that felt such was "typical" of expressing "intimate intercourse" or "benefits in general," but disagrees with that view, noting as well the specialness of dining with royalty.
The Referent in Ps 41:9
Now some commentators say the model behind the Ps 41:9 betrayer is Aithophel:
My own familiar friend; probably he means Ahithophel, who had been his bosom-friend and prime-minister of state, in whom he trusted as one inviolably firm to him, whose advice he relied much upon in dealing with his enemies, and who did eat of his bread, that is, with whom he had been very intimate and whom he had taken to sit at the table with him, nay, whom he had maintained and given a livelihood to, and so obliged, both in gratitude and interest, to adhere to him.1
But here David had in mind the treachery of his friend Ahithophel, who
betrayed him, and then hanged himself (2 Sam. 16:20–17:3, 23).2
But Mephibosheth contextually appears to be a far more likely referent. The Psalm in its entirety considers a multitude of betrayers (see v.5, 7), and no doubt behind it includes prominent men such as Absalom, Aithophel, and others. But the Psalm does narrow to this particular one in v.9, "even my own familiar friend." Now consider these points in favor of the referent behind the Psalm being Mephibosheth:
- From the above parts in 2 Samuel, there is a clear understanding that Mephibosheth had a prominent place at David's table.
- Mephibosheth had no doubt become (at least from all appearances) a friend, for he was eating daily with David when he was in Jerusalem, which in his later reign was fairly constant, as he no longer went to war. Also, being the son of Jonathan, David essentially took him in Jonathan's place—so David was friendly toward him to start.
Ziba's claim about Mephibosheth was specifically in reference to a heart of betrayal and usurping of David, stating (2 Sam 16:3b):
“Indeed he is staying in Jerusalem, for he said, ‘Today the house of Israel will restore the kingdom of my father to me.’ ”
- David originally believed Ziba, initially granting all Mephibosheth's land to him because of the apparent betrayal (2 Sam 16:4); so David, at least for the time he was displaced by Absalom from Jerusalem, thought himself betrayed by even the one who he had shown such mercy and kindness to, the son of his dear friend Jonathan.
- Psalm 41 opens with a prayer to God to be merciful to and bless those who consider the poor (v.1-3). This pictures precisely what David had done in the case of Mephibosheth; a picture that does not match that of Ahithophel, who appears from the text to be a man of some wealth and means such that he felt things needed to be put in order before committing suicide (2 Sam 17:23). Additionally, it provides some context as to why the mention of being good to the poor relates to the points later in the Psalm regarding the acts of betrayal.
David, upon returning to Jerusalem, shows that a nagging question on his mind while in exile was that one first posed upon meeting Mephiobosheth again (2 Sam 19:25):
“Why did you not go with me, Mephibosheth?”
If these historical and literary contextual points are accurate in pinpointing Mephibosheth as the prime referent to v.9, then that specifically places this Psalm's composition during David's exile from Jerusalem when Absalom took over (i.e., before the return and David's ability to get Mephiobsheth's side of the story).
Sitting at a king's table, especially regularly, meant "a much greater depth of friendship," and that is the context of Psalm 41. Such a view cannot be fully extrapolated to ordinary people, though again, if one has an enemy, it is not likely they will be sitting to eat with you; and anyone who eats regularly with another is probably of a closer friendship than mere acquaintance.
As to the sub-question, that was already answered quite well by Soldarnal, that Jesus saw the statement as prophetic of himself, as John 13:18 notes.
1 Matthew Henry, Matthew Henry’s Commentary on the Whole Bible: Complete and Unabridged in One Volume (1710; Peabody: Hendrickson, 1994).
2 Allen P. Ross, “Psalms,” in The Bible Knowledge Commentary: An Exposition of the Scriptures, edited by J. F. Walvoord and R. B. Zuck (Wheaton, IL: Victor Books, 1985).