The most common way to congratulate somebody after a simcha (a happy moment) in that person’s life is Mazal tov. A Bar/Bat mitzvah, the birth of a child or grand child, a wedding or any other special moment deserves the good wishes of Mazal tov.
Sometimes we even joke and say Mazal tov when something breaks in the kitchen (a plate or a cup, etc.), perhaps because the noise evokes the sound of a groom breaking the glass under the chuppah (the wedding canopy).
There are events in our lives that are more frequent and (maybe) less relevant than a birth or a marriage like leading a service, saying a D’var Torah or receiving an aliyah. We have two different options to congratulate those who have had these kinds of honors: The Ashkenazi custom is to say: Yasher Koach (יישר כוח) that means literally “may your strength be firm.” The answer to this blessing should be Baruch Tiyihe (ברוך תהיה), may you be blessed. The Sephardic custom is to say Chazak u Baruch (חזק וברוך) that means literally “strong and blessed.” The answer to this blessing is Chazak vEmatz (חזק ואמץ), strong and courageous.
The first mention of this form of congratulation is in the Talmud. It is written that when Moses broke the tablets G-d agreed with him and said: Yasher Koach that you broke them" (Shabbat 87a).
It is not very clear the path that this phrase went through until it became the most used form of congratulation after receiving an aliyah. Probably in ancient times, when few people had their own books, the Torah had to be read while it was standing upright and the text had to be visible to the congregation. People approached the center of the synagogue surrounding the reader. The reader, therefore, had to physically sustain the scroll by taking hold of its posts. Yasher koach became an encouragement to the reader, "May you have strength not to cause the Torah to fall.”
It is very interesting to relate the current usage of the phrase to the original Yasher koach. Today’s usage of this phrase is paradoxically a reversal of the actual usage as G-d reassured Moses by saying: You have done the right thing in showing the strength and bravery to hurl the Torah before a people that has proven itself unworthy of it.
Did you know that? Now you know something more about our tradition, Yasher Koach!!!