Shavuot

The joy of Chag Shavuot. Can you shower on Shabbat and Yom tov? What are the Halachot for those who Remained Awake all night?

In general there are 3 ways of coming close to God: most common, either through emotion or intellect, but then Judaism adds: or to be "similar" [=close] to Him. The greatest gift that He could give us is the "Tzelem Elohim", or capability of imitateo dei, being Godly. The she'ur discusses the advantages & disadvantages of each approach to Him. Most importantly, we can't understand His Essence, but we can amd should understand His actions. This is the ultimate in both the Rambam's rational and also the kabbalistic approach to Judaism. Rav Kook explains that the 13 traits of God, as well as the 10 sfirot, all detailus what to emulate. This has far-reaching ramifications for prayer, study as well as defining our goal and potential in life!

On the holiday of Shavuot, is the practice of learning Torah all night long a commandment or a just a custom?

Every holiday is dependent, so to speak, on memory for its observance to be meaningful and uplifting.

Why do we make an eruv tavshillin? What is the recipe? What should I do if I forgot to make one?