Why do we have Sunnah and supererogatory Salaat?

<p class="MsoNormal"><span style="font-family:Verdana;mso-bidi-language:ER"><br /> <br /> If the slaves of Allah remain steadfast on the obligations, keep their affairs clean and clear, keep in mind the commendable acts and also offer supererogatory worship, then it will be a means of spiritual growth for them and will result in high stations in paradise and also gain them the pleasure and approval of Almighty Allah.</span><br /> <span style="font-family:Verdana"><br /> There is a Hadith in Sahih Bukhari:</span></p> <p class="MsoNormal"><span style="font-family:Verdana;mso-bidi-language:ER"> </span><span style="font-family:Verdana">Translation: My slave comes closer to me with no act more beloved to me than the obligatory acts of worship (<i>Fardh</i>) which I have assigned to him and my slave keeps coming closer to me with supererogatory acts of worship (<i>Nafl</i>), so much so that I start loving him.<span style="mso-spacerun:yes">&nbsp; </span>When I make him my beloved, then I become his ears with whom he hears.<span style="mso-spacerun:yes">&nbsp; </span>I become his eyes with which he sees.<span style="mso-spacerun:yes">&nbsp; </span>I become his hand with which he holds and I become his legs with which he walks.<span style="mso-spacerun:yes">&nbsp; </span>If he asks me for something, I surely grant it.<span style="mso-spacerun:yes">&nbsp; </span>If he asks me for protection, I surely grant it.<span style="mso-spacerun:yes">&nbsp; </span>If I want to do something, I don&rsquo;t hesitate the way I wait before taking the soul of the faithful when does not desire it and I don&rsquo;t like hurting him.<span style="mso-spacerun:yes">&nbsp; </span>(Sahih Bukhari, Hadith No. 6502)</span></p> <p class="MsoNormal"><span style="font-family:Verdana">&nbsp;</span></p> <p class="MsoNormal"><span style="font-family:Verdana">Apart from Obligatory Salaat, Sunnah and supererogatory Salaat have been decreed for various times of the day:</span></p> <p class="MsoNormal"><span style="font-family:Verdana">&nbsp;</span></p> <p class="MsoNormal"><span style="font-family:Verdana">(1)<span style="mso-spacerun:yes">&nbsp; </span>Before the Obligatory Salaat.</span></p> <p class="MsoNormal"><span style="font-family:Verdana">&nbsp;</span></p> <p class="MsoNormal"><span style="font-family:Verdana">(2)<span style="mso-spacerun:yes">&nbsp; </span>After the Obligatory Salaat.</span></p> <p class="MsoNormal"><span style="font-family:Verdana">&nbsp;</span></p> <p class="MsoNormal"><span style="font-family:Verdana">(3)<span style="mso-spacerun:yes">&nbsp; </span>At other times like Salaat Ul Ishraaq after dawn, Salaat Ul Chaasht after the sun rises over head, Salaat Ul Awwabeen in the early part of the night, Salaat Ul Tahajjud in the middle or last part of the night.</span></p> <p class="MsoNormal"><span style="font-family:Verdana">&nbsp;</span></p> <p class="MsoNormal"><span style="font-family:Verdana">There are many benefits of Sunnah and supererogatory Salaat before the Obligatory Salaat.&nbsp; One remains busy in the various affairs of the world.<span style="mso-spacerun:yes">&nbsp; </span>Usually, all those other engagements make one heedless of the remembrance of Almighty Allah and become impediments to it.<span style="mso-spacerun:yes">&nbsp; </span>This in turn allows the desires to raise their head.<span style="mso-spacerun:yes">&nbsp; </span>When these take root, the angelic faculty is suppressed by them.<span style="mso-spacerun:yes">&nbsp; </span>Thus, because of being busy in worldly affairs, one is ensnared by these desires.<span style="mso-spacerun:yes">&nbsp; </span>This in turn affects the heart and the soul and darkens them.</span></p> <p class="MsoNormal"><span style="font-family:Verdana">&nbsp;</span></p> <p class="MsoNormal"><span style="font-family:Verdana"><span style="mso-tab-count: 1">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </span>For this reason, Sunnah and supererogatory Salaat have been decreed which cleanse the heart and the soul and increase one&rsquo;s concentration and devotion.</span></p> <p class="MsoNormal"><span style="font-family:Verdana">&nbsp;</span></p> <p class="MsoNormal"><span style="font-family:Verdana">It is mentioned in Al Bahr Ur Raaiq Sharh Kanz Ud Daqaaiq:</span></p> <p class="MsoNormal"><span style="font-family:Verdana">&nbsp;</span></p> <p class="MsoNormal"><span style="font-family:Verdana">Translation: The Sunnah have been decreed to complete the obligatory forms of worship. </span></p> <p class="MsoNormal">&nbsp;</p>