Yosef symbolizes Shmiras Ha'Bris, and perhaps the biggest lesson that we can learn from him was that it was only through the merit of his "withholding" that he merited that so much bounty and goodness should flow forth through him. And this is the secret of the divine channel of Yesod. When we close all the holes in our divine "pipes" (and we are willing to go through the dryness of "Tamuz" first), Hashem's blessing and bounty is able to flow through us properly.
The Koach of the Bris is somewhat like a nuclear reaction. Our job is to take this "nuclear power" and harness it for constructive purposes; to bring forth life, not death. How is this done in a reactor? By inserting fuel rods into the reactor's core to absorb and "hold back" the nuclear chain-reactions from continuing. By doing this, we are able to harness the tremendous energy, and we are able to light up entire cities with electricity! Our enemies on the other hand, want to harness nuclear power for destructive purposes. This happens in atomic weapons, where their is no "containment" of the nuclear reactions. The Jewish people succeeded in destroying the nuclear reactor "Tamuz" of Saddam, on erev Shavuos, the 5th of Sivan, 1981, in the month of Yakov Avinu. Shavuos is the time of kabbalas Hatorah, and the Torah is like the "fuel rods" that teach us how to harness the power of the Yesod properly through the Mitzvos. The Mitzvos of the Torah, such as "Pru u'revu - be fruitful and multiply" on the one hand, and "lo sikrivu legalos erva - do not come close to revealing nakedness" on the other, teach us how to channel Hashem's bracha in the right ways and harness the tremendous energy of Yesod for the good.
The Yetzer Hara wants us to use the potent power of the Bris for destructive purposes. But through the power of Shmiras Habris, by withholding this potent energy and harnessing it for constructive purposes only, we become vessels for divine bounty, and we succeed in "containing" the designs of our enemies, who once again desire to use nuclear power to destroy us...
And that is the beauty of the seeming contradiction of Tamuz. And that is perhaps the reason why Yosef was born on Rosh Chodesh Tamuz. Let us harness the tremendous power of Yosef on his Yartzeit today, by properly "containing" the power of Yesod and thereby harnessing it for LIFE and endless divine blessing.