Our parsha opens with the korban tamid, which has a special mitzvah: "The priest shall kindle wood upon it every morning." (Vayikra 6:5)

The Gemara (Yoma 26b) derives from the pesukim that the morning tamid requires two blocks of wood in the hands of one kohen, whereas the evening tamid requires two blocks of wood in the hands of two kohanim. The Gemara does not explain, though, the distinction between the morning tamid and that of the evening.

There is another difference between the two temidim. In Yechezkel it says: "You shall prepare a sheep ...  as a daily burnt-offering for Hashem; you shall make it every morning." (46:13) Radak notes that the evening tamid is not mentioned there, and writes that in the future the tamid will only be offered in the morning and not in the evening.

I heard from Rav Shlomo Fisher shlita a wonderful explanation of this.

Chazal disclosed that the morning offering comes to remind the merit of akeidat Yitzchak. It says in the Mishna Tamid (ch. 4): "They would not tie the lamb, but rather bind [its fore and back legs]," and the Gemara explains, "like the binding of Yitzchak, son of Avraham." It further says in Parshat Tzav, "he shall prepare the burnt-offering upon it, and burn the fats of the peace-offering on it." This teaches that the morning tamid precedes all the other sacrifices; i.e., all of the sacrifices should follow the morning tamid, in order to mention the merit of Yitzchak in all of them.

The evening tamid, on the other hand, comes to atone for the sin of the golden calf. Therefore, its time is from six hours (midday) and on, just as it says about the golden calf, "The people saw that Moshe delayed (boshesh) in coming," (Shemot 32:34) as Chazal comment: "boshesh – ba shesh," the sixth hour came and Moshe did not arrive. In every generation there is something of the sin of the egel, as Chazal explain the verse: "On the day of My reckoning, I will reckon." (Shemot 32:34) Thus, in the future, the sin of the golden calf will be atoned for, and there will no longer be a need for the evening tamid.

The Gemara in Sanhedrin (102a) says that until the time of Yerovam, Bnei Yisrael "nursed" from one calf, and from Yerovam's time and on they "nursed" from two or three calves. Rashi explains that at first they were punished for the sin of one calf, and from Yerovam and on they were punished for three calves, i.e., also for the two that Yerovam made.

Yerovam's calves are something not understandable, one of G-d's secrets. When Rechavam King of Yehuda came to fight against Yerovam, and to reunite the kingdom, the prophet Shemaya says to him: "Thus says Hashem: "Do not go up and do not battle your brethren Bnei Yisrael. Return each man to his house, for this matter was from Me." (Melachim I 12: 24) Immediately afterwards, Yerovam makes the two golden calves. This was revealed and known to G-d, and even so He told Rechavam that he should not go fight against Yerovam. This must also have been included in, "this matter was from Me," and apparently this was part of the punishment of the golden calf.

Based on this, Rav Fisher explained why the morning tamid was offered with two blocks of wood in the hand of one priest, whereas the evening tamid was offered with two blocks in the hands of two priests. The division of the kingdom is alluded to by the two pieces of wood, as it says in Yechezkel: "Take for yourself one piece of wood and write upon it, 'for Judah' ... and take one piece of wood and write upon it, 'For Joseph' ... Then bring them close to yourself, one to the other ... and they will become united in your hands." (37:16-17) Thus, for the morning tamid, which indicates the perfected world of the future, one priest unites the two pieces of wood. The evening tamid, on the other hand – which comes to atone for the sin of the golden calf – alludes to the imperfect state, that the two pieces of wood are separate, and therefore two priests bring the two pieces of wood.

In the future, the sin of the golden calf will be rectified, and unity will return to Am Yisrael. No longer will the evening tamid be offered, but only the morning one, in which the two blocks of wood will be unified in the hands of one kohen. Yechezkel's prophecy about the unity of the tribes will be fulfilled.