According to the words of the Ramban, the Torah gave two ways in the mitzvah of removing leavened bread, either to nullify it in one's heart or to burn it. It should be explained why we follow both ways and not suffice with one of them, as is ruled in the Shulchan Aruch (Orach Chayim, Siman 434, Seif 2): "After checking, immediately at night one should nullify it and say: 'Any leaven that is in my possession, which I have not seen and have not removed, shall be nullified and be considered as dust of the earth.' Rema: And one should say the nullification in a language that he understands, etc. It is good to nullify it again on the fourteenth day, at the end of the fifth hour, before the sixth hour arrives, as once the sixth hour arrives it is prohibited and one cannot nullify it. Rema: And one should not nullify it during the day until after he has burned the leaven, in order to fulfill the mitzvah of burning his leaven." The Mishnah Berurah (Sk 12) writes on this that therefore one must burn it and also nullify it before the sixth hour. This is also clarified later in the Shulchan Aruch (Siman 454, Saif 1): "How is the removal of leaven done, burn it or crumble it and throw it to the wind or into the sea, etc. Rema: The custom is to burn it. And it is good to burn it during the day, similar to when it was left over and burned during the day. But if one wants to burn it immediately after checking so that it doesn't become a burden, he has the authority to do so." The Mishnah Berurah adds (Sk 7): "The Maharil wrote another reason, that it is more correct to burn it during the day so that through this one will remember to nullify it on the day. And they burn it at the fifth hour, as one needs to nullify it afterward, and by the sixth hour it is no longer in his possession to nullify." - So why do we practice fulfilling the mitzvah of removing leaven in both ways?