"Do not ruin (or destroy) David, the conqueror. As it is written (Ecclesiastes 4:9), 'Two are better than one.' They are better off as two, rather than one who goes alone. If one falls, the other can help him up. (Ecclesiastes 4:10) And if someone attacks one, the other can defend him.
And if a person does evil to them, they can resist him. And if they are three, it is even better, as it says (Ecclesiastes 4:12), 'A threefold cord is not quickly broken.' Another thing is that two righteous people are better than one righteous person or one wicked person. The merit of two righteous people is not comparable to the merit of one righteous person.
They will receive good reward. If calamity befalls the family, the merit of both of them stands and cancels it, as it says (Jeremiah 3:14), 'I will take one from a city and two from a family.' Because of two from the same family, that family prospers. And if there were three righteous people, even if it is a righteous son of a righteous son of a righteous person, their merit will never cease."
As it says (Kohelet 4:12), "And the threefold cord." They said before Rabbi Zeira, "But wasn't so-and-so a righteous man, son of a righteous man, son of a righteous man, and [yet he lived] in a generation of wicked people?" He said to them, "He will not be quickly uprooted, even if he falls [he will rise again], as was done with so-and-so." As it says (Isaiah 59:21), "My words which I have put in your mouth shall never depart from your mouth, nor from the mouth of your children, nor from the mouth of your children's children."
Since he [the righteous person] is a son of Torah, and his son and his son's son [are also righteous], then Torah will never cease from them. As it says (Jeremiah 31:34), "Forevermore." What is it [referring to]? The Lord said, "I vouch for this matter."
Another interpretation: "Two are better than one." [This refers to] two who study the Torah together and discuss [its teachings] among themselves. And if there are three [who study together], then it is even better. As it says (Kohelet 4:12), "And the threefold cord." Another interpretation: "Two are better than one."
This refers to Michal, daughter of Saul, and Jonathan, who both loved David and saved him from Saul, her father. It is written about Michal (1 Samuel 18:28), "And Michal, Saul's daughter, loved him [David]." And about Jonathan it is written (1 Samuel 18:1), "And Jonathan loved [David] as his own soul." Michal saved [David] from the house [of Saul], and Jonathan from outside.
"Two are better than one" [refers to them], and "the threefold cord" [refers to] the people of Israel, as it says (2 Samuel 19:40), "And all Israel and Judah loved David." To the conductor, do not destroy [a psalm].