On the festivals (Pesach, Shavuos, and Sukkos) Jewish men are commanded to visit the Temple and are forbidden to do so without bringing a burnt-offering, as it says "[Three times a year] all your males shall be seen before Ha-Shem your G-d... [on the festival of unleavened bread and on the festival of weeks and on the festival of booths]; and he shall not be seen before Ha-Shem empty".¹ They are also commanded to bring many peace-offerings then, as it says "[You shall slaughter a Passover to Ha-Shem your G-d, sheep and cattle... you shall make a festival of weeks to Ha-Shem your G-d according to the gift of your hand that you give... you shall make yourself a festival of booths...] and you shall rejoice on your festival... seven days you shall make a festival to Ha-Shem your G-d".² The commandment to rejoice applies also to women and to those who are unable to visit the Temple. One should share these offerings with the poor and unfortunate and especially with the Levite, as it says "[You shall rejoice in your festival, you and your son and daughter and slave and maidservant] and the Levite and the stranger and the orphan and the widow".³ It is forbidden to abandon the Levite, as it says "Beware lest you abandon the Levite".^4,a

On the Sukkos just after the sabbatical year all Israel must gather together to hear the Torah read, as it says "At the end of seven years at the time of the sabbatical year on the festival of booths when all Israel comes to be seen [before Ha-Shem... you shall read this Torah before all Israel in their ears]; assemble the nation, the men and the women and the children and your stranger that is in your gates, [in order that they may hear...].^5,b

Sources:
1. Deut. 16:16, see Ex. 23:14-15 and 34:23	a. 1:1; 2:4,14; see Korban Pesach 10:12
2. Deut. 16:2,10,13-15	b. 3:1
3. Deut. 16:14; see 16:11
4. Deut. 12:19
5. Deut. 31:10-12