Below is a link to the book, “Moadim B’Simcha” on the Jewish Holidays by HaRav Shlomo Aviner. The chapters of the book follow the holidays throughout the year. Founder and Head of the Ateret Yerushalayim Yeshiva in the Old City, HaRav Aviner also served for several decades as the Rabbi of Bet-El Alef. He is the author of 150 books on a wide range of Jewish themes and has pubished thousands of articles and responsa on Halacha. He is considered one of Israel’s foremost experts on the teachings of HaRav Avraham Yitzhak Kook and HaRav Tzvi Yehuda Kook, his mentor for many years. More of his books and writings can be found on the website: http://www.ravaviner.com/
Here is the link to the full text of his book on the Jewish Holidays.