(Isa. 2:6; Ex. 23:32; Deut. 7:1–9)
Hebrew sepiyqu means to “clasp hands” rather than the KJV “please themselves.”
(Donald W. Parry, Jay A. Parry, and Tina M. Peterson, Understanding Isaiah [Salt lake City: Deseret Book Co., 1998], 29.)
The tenderness of the bond which united Jewish parents to their children appears even in the multiplicity and pictorialness of the expressions by which the various stages of child-life are designated in the Hebrew. Besides such general words as “ben” and “bath”—“son” and “daughter”—we find no fewer than nine different terms, each depicting a fresh stage of life. The first of these simply designates the babe as the newly-“born”—the “jeled,” or, in the feminine, “jaldah”—as in Ex. 2:3, 6, 8. But the use of this term throws a fresh light on the meaning of some passages of Scripture. Thus we remember that it is applied to our Lord in the prophecy of His birth (Isa. 9:6): “For a babe (‘jeled’) is born unto us, a son (‘ben’) is given to us;” while in Isa. 2:6 its employment adds a new meaning to the charge: “They please themselves (or strike hands) with the ‘jalde’—the ‘babes’—of strangers”—marking them, so to speak, as not only the children of strangers, but as unholy.
(Alfred Edersheim, Sketches of Jewish Social Life [Peabody, Massachusetts: Hendrickson Publishers, 1994], 99.)
The term … translated strangers, means foreign as in opposition to the son or lawful heir. In Ecclesiastes 6:2, the feminine form of the word is used to refer to a strange woman as in opposition to one’s own wife, especially with regard to illicit intercourse; hence an adulteress… . The people had become strangers to the House of the Lord. Therefore, the term also was used to signify the worship of idols or strange gods. Yet, a most interesting term is the word “please.” … The Jerusalem Bible translates the phrase, “they clap foreigners by the hand.” That interpretation is footnoted by the comment, “by the hand”; signifies, “a gesture of friendship, or else a magic rite: the text is obscure.” The whole phrase may be taken several ways and has multiple meaning. It may be taken as a condemnation of association with harlots, foreign gods, persons who worship idols, or marrying or being in league with followers of idols. Yet, even further, Isaiah may have also been condemning those who clap hands with strangers in secret rites, delivering sacred things to those not worthy to receive them. The Hebrew term translated “please” means to strike, to clap the hands, or to make an agreement concluded with the striking of the hands or handshake. They left God, turned unto soothsayers and “strangers”. They served the gods of this earth. Silver and gold became gods. Collecting treasure became the objective of life.
(Loren D. Martin, Isaiah: An Ensign to the Nations [Salt Lake City: Valiant Publications, 1982], 62–63.)