17 Three times in the year all thy males shall appear before the Lord God.
18 Thou shalt not offer the blood of my sacrifice with leavened bread; neither shall the fat of my sacrifice remain until the morning.
19 The first of the firstfruits of thy land thou shalt bring into the house of the Lord thy God. Thou shalt not seethe a kid in his mother’s milk.
We are told that all the males must present themselves before the Lord at the tabernacle three times in the year. Given that we just heard about three feasts to be observed in a year, it may very well be that this mass gathering would coincide with those celebrations.
This would certainly make Israel a well measured nation. On a regular basis they would have a sort of informal census, seeing exactly what their maximum military strength and workforce was. This would also require the people to remain a close-knit society. Being required to regularly travel to one central location would mean that they could not spread themselves too far from their center, and on a regular basis they would see one another in close company. Separation, distinction, and rivalry would therefore all be deterred.
Also, it would seem, they were not to come to this great gathering empty-handed. The assumption is that these following verses about appropriate sacrifice are referencing these three gatherings in the year, and that every man would come to the Lord with something to offer. They would bring offerings of firstfruits or offerings of livestock, perhaps according to which feast was being observed or according to the man’s occupation.