Why disguise?

B"H

Bamidbar (Numbers) Ch. 21:1 reads as follows:
וישמע הכנעני מלך ערד ישב הנגב כי בא ישראל דרך האתרים

Loosely translated:
And the Canaanite king of Arad, who dwells in the Negev, heard that the Jews arrived through Atarim.

Rashi brings an interesting interpretation that the Amalekites were the ones who attacked the Jews at this point, but they disguised themselves as Canaanites by speaking the Canaanite tongue. (Some versions of Rashi, as well as other sources such as Yalkut Shimoni, hold that the Jews also changed their dress to that of the Canaanites.) Whatever the exact disguise was aside, Rashi points out the reason for the disguise: So that the Jews pray to Hashem to save them from the Canaanites and since they were in reality battling Amalek, the Jews' prayers would have no effect.

So a question stands out here:
If Amalek wanted to deceive the Jews so that their prayers are off-target then why did they not employ the same deceptive tactic in Shmot (Exodus) 17:8, as it is written:
ויבא עמלק וילחם עם ישראל ברפידם (=And Amalek came and battled with the Jews in Refidim)? Clearly they didn't attempt to disguise themselves in this case.

So, what's the difference between the first battle in Shmot 17:8 and the second one in Bamidbar 21:1?

An explanation:
In the first battle the Jews were fresh out of Egypt. Ahead of them was 40 years (in hindsight) of miraculous existence: the food was taken care by Mana, the water by Miriam's portable well, the clothing grew with them, the land ahead of them was flattened by the clouds of glory, etc... They were totally exempt from worldly-worries. The analog nowadays is a Jew living his/her entire life in the 4 cubits of Torah study -- shunning away from involvement with the mundane world.

At this time comes Amalek, undisguised, and does battle with the Jews. More than a purely physical battle, this was an ideological battle: the Amalekite's claim was that both Jews and Amalek come from the same forefather Abraham. Their issue with the Jews was the preferential treatment that the Jews are being given. After all the Jews and the Amalekites were cousines, why is it then that the Jews can live this miraculous life and the Amalekites cannot. Perhaps G-d forbid, the Jews don't deserve this either? Perhaps the Jews are like any other nation out there? The attack was on the Jew's belonging in the 4 cubits of Torah.

To make such claims, the Amalekites needed to come as themselves -- the grandchildren of Abraham. They of course lost that battled proving once-and-for-all that a Jew does indeed belong in the 4 cubit of Torah.

However, Amalek was defeated but wasn't out yet. Amalek was just waiting for another opportunity to battle the Jews. The opportunity presented itself in this second battle: the Jews were about to enter the land of Cannaan (=Israel). What's ahead of them is many centuries of working the land, paying the mortgage, selling one's ware at the market place, etc... In other words, mundane daily existence.

Comes Amalek and says, the battle over miraculous existence we lost, but now you're entering a phase of mundane existence. We will do battle again! To make such a declaration they disguised themselves as Canaanites, dwellers of the ארץ כנען (=the land of Canaan), representing ארציות (=mundane life).

Of course they lost the second battle as well. Their mistake: divine providence extends beyond the 4 cubits of Torah, even into the lowest levels (i.e., ארציות) of Jewish existence.

This teaches us that even when a Jew is involved in mundane life he should maintain his connection to the divine, for that's where his protection comes from. As a matter of fact, he/she is given the opportunity to infuse the mundane daily life with the holiness of Torah through the performance of physical mitzvot (commandments) thereby fulfilling the verse "בכל דרכך דעהו" (=Know G-d in all your dealings.)

Good Shabbos!