The Gemara in Masechet Shabbat (118) cites Rabbi Yossi's remark expressing his wish that he would have the same portion in the world to come as those who "complete the Hallel every day." While this at first glance appears to refer to the Hallel text that we recite on the holidays, the Gemara clarifies that this is not the case, for to the contrary, it is improper to recite Hallel every day. Rather, Rabbi Yossi refers here to what we call Pesukeh De'zimra – the final chapters of Tehillim which we recite each day as an introduction to our prayers. Rashi, in his commentary to the Gemara, explains that the Gemara speaks of specifically two chapters – chapter 148 of Tehillim ("Halelu Et Hashem Min Ha'shamayim") and the final chapter of Tehillim, chapter 150 ("Halelu Kel Be'kodsho"). Others, however, explain that the Gemara refers to the final six chapters, starting from chapter 145 (what we call "Ashreh"). It seems likely that Rashi agrees that all six chapters should be recited, but he sought to emphasize the unique importance of chapters 148 and 150. (Chapter 148 is special in that it describes the entire earth – the heavens, the sun, the moon, the stars, and all the creatures in the world – giving praise to G-d. One Rabbi said that when we recite this chapter, we serve as the conductor of the symphony, instructing everything in the universe to come together to sing the Almighty's praises.) In light of Rashi's comments, the Poskim write that if a person is unable to recite all of Pesukeh De'zimra, he should at least endeavor to recite chapters 148 and 150, given their unique importance. Indeed, in some editions of the Siddur, these chapters are written in bold or a special font to emphasize their special significance. Several different reasons are given for the reason why we recite Pesukeh De'zimra before we come forward before G-d to pray for our needs. Some explain based on the Gemara's teaching (Berachot 31a) that a person should be in the right mood when praying – specifically, in a mood of "Simha Shel Misva," the joy of a Misva. One should not pray when he is angry, upset, agitated, or frivolous, but rather when he feels content and gratified as a result of a Misva. The Sages therefore instituted that we introduce our prayer with the recitation of chapters of Tehillim to put us in the right mood and the proper frame of mind for Tefila. Another explanation is that it is proper to first give praise to G-d before presenting our requests. We learn this format from Moshe Rabbenu, who, before asking for permission to enter the Land of Israel, praised G-d for the great miracles He performed (Debarim 3:24). Therefore, before we approach G-d to ask for our needs, we first spend some time speaking His praises, just as Moshe did. The Rabbis of Kabbalah taught a different reason for reciting Pesukeh De'zimra. The verb "Z.M.R." can mean "sing," but also "prune," as in the Torah's command "Ve'charmecha Lo Tizmor" (Vayikra 25:4), which forbids pruning during the Shemita year. As our prayers ascend to the heavens, they are exposed to the negative spiritual forces that seek to sabotage our Tefilot. We neutralize these forces through the recitation of the beautiful praises in these chapters of Tehillim, and thus this recitation is called "Pesukeh De'zimra" – the verses that "prune," or eliminate, the harmful spiritual forces that threaten our prayers.