The distinction between the three groups is immediately apparent from the Torah description of how Moshe warned Pharaoh before each of the plagues. By the first plague, Moshe is told to *go* ("Lech") to the Nile river at daybreak and forewarn Pharaoh of the imminent plague of Blood (Shmot 7:14). By the following plague, however, Moshe is simply told, "*Come* ("Bo") to Pharaoh" (7:26), which the Midrash interprets as "Come to Pharaoh's *palace*" -- the place where Pharaoh would be expected to hold audiences (Pesikta Zutrati 7:26. This seems to be the consensus of the early commentaries as well -- see Ramban 8:15; Rabbenu Bachya 10:1; etc.). The third plague (Lice) came without previous warning. This pattern repeats itself in plagues #4,5,6 (Shmot 8:16, 9:1, 9:8) and #7,8,9 (Shmot 9:13, 10:1, 10;12).

Why warn Pharaoh in two different places? Rabbenu Bachya (10:1) explains that Pharaoh was particularly haughty with regards to the Nile river ("My river is mine..."- Yechezkel 29: 3), and with regards to his beautiful palace (the palace was a common expression of a king's arrogance -- see Daniel 4:1). This is why, after the plague of Blood, "Pharaoh turned and came to his palace, [whereupon he returned to being his proud self] and didn't heed the [miracle]" (Shmot 7:23). For this reason, it was specifically in these very places that Hashem chose to humble Pharaoh, and warn him of the plagues. (Malbim 7:14 and Abravanel 7:26 also address this issue and propose opposing solutions, which we shall not discuss here.)

Why is Pharaoh not warned at all before the third plague? Rabbenu Bachya (ibid.) suggests that by the third plague of each group, Pharaoh could be compared to a criminal who has twice been caught sinning. If a person sins twice,, even after being warned in advance that what he is doing is illegal and punishable, then the third time he may be punished without prior warning (see Sanhedrin 81b)!

1) Chizkuni (7:15) suggests that "Bo" implies, "Come to me!" Hashem would be waiting for Moshe at the palace. However, the Divine Presence of Hashem didn't "wait" for Moshe by the river. Why was that?

Rashi (Shmot 7:15) tells us that Pharaoh tried to convince the Egyptians that he was a deity, and did not need to tend to such humanly needs as relieving one's self. The way he accomplished this was by leaving the palace early in the morning, all by himself, and going alone to the Nile River. (Presumably, Pharaoh told his guards that he was going to "bless" the Nile River -- see Rashi Bereishit 47:10). There, with nobody watching, he would defecate. Moshe was told to go and greet Pharaoh in the morning by the Nile, where Pharaoh had gone to heed the call of nature. This embarrassing exposure of Pharaoh's mortality was all part of Pharaoh's lesson.

If so, it is obvious why Moshe was not told to "come" to the Nile. Since there was excrement nearby, it could not be said that "Hashem would be waiting for him there." The Divine Presence does not rest in a place where there is human wastes (Devarim 23:13-15)!

2) Salmah Chadashah (R. Shlomo Sobel, a "Maggid" [= public orator] in Jerusalem ~1948) proposes another solution. According to the Midrash, the palace of Pharaoh was entirely surrounded by armed guards and trained animals, to protect the king from unwanted visitors. When Moshe went to the palace, Hashem wanted to encourage Moshe Rabbenu not to be daunted by these deterrents. Hashem Himself would be with him, telling him "Come with me", and ushering him safely into the palace.

If so, this may be what Hashem meant by saying, "*Come* to Me, by Pharaoh." When Moshe stood before Pharaoh in the king's court, he felt as though he was standing before the Divine Presence. Although Pharaoh was wicked, he was a king nonetheless (as in Rashi to Shmot 11:8).

However, the majesty of a king which brings to mind the majesty of Hashem could not be said to be displayed when King Pharaoh was at the Nile River. There, Pharaoh was alone without the palace environment and without his royal entourage, simply to heed the call of nature. This, then, is why Moshe was told to *go*, away from the Divine Presence, to the Nile!