The Roke’ach (quoted by the Rama in his notation on Chapter 95) writes that before beginning to recite the Amida prayer, one should take three steps back, then take three steps forward (to one’s original place), and then stand there and begin praying silently. The reason for this is because this resembles an endearment and readiness to perform the matter at hand similar to when Moshe wished to pray to Hashem, he entered three partitions of darkness, cloud, and fog. This custom is quoted by the Kenesset Ha’Gedolah and other great Acharonim.
Although the Eliyah Rabba writes that there is no need to observe this custom since it is not mentioned in the Talmud or in the works of most Rishonim, nevertheless, the Mishnah Berura writes that the prevalent custom is to do so. Hagaon Rabbeinu Yosef Haim writes in his Sefer Ben Ish Hai (Parashat Beshalach) that there is a great reason behind this custom of taking three steps back and then taking three steps forward before praying according to the Kabbalah.
On the other hand, some say this custom is correct only when one is sitting and learning in a Bet Midrash or at home and suddenly realizes that the time for prayer has arrived, for in this case, one must take three steps back in order to prepare somewhat for prayer. However, if one has already taken many steps by walking to the synagogue to pray, one need not be meticulous regarding this custom.
Hagaon Peri Megadim writes that although one who has walked to the synagogue need not observe this custom, nevertheless, since this does not involve great difficulty and effort, it is preferable to do so.
Halachically speaking, those who customarily take three steps back and forward before praying shall surely be blessed; however, many great Sephardic luminaries were not meticulous regarding this custom at all, for they relied upon the Poskim who did not mention this custom or because they relied on the steps they took while walking to the synagogue. Indeed, we have observed that when Maran Rabbeinu Ovadia Yosef zt”l stood to pray in the exact location where he was sitting and praying right before, he would not take three steps back or forward before praying and he would act in accordance with Maran Ha’Shulchan Aruch and other Poskim who did not mention this custom at all.