And thou shall show thy son in that day,.... On the first of the days of the feast of unleavened bread, the reason of eating it; and this is to be shown not to a son or single child only, but by parents to all their children, sons and daughters, and even unasked, as Maimonides (b) interprets it; and so Jarchi's note is, to a son that knows not how to ask or what to ask about; see Gill on Exodus 12:26, Exodus 12:27,

saying, this is done because of that which the Lord did unto me, when I came forth out of Egypt: that is, this unleavened bread is eaten because of the quick and speedy deliverance of Israel out of Egypt, so that they had not time to leaven their dough.

(b) Hilchot Chametz Umetzah, c. 7. sect. 2, 3.

"because of that which Jehovah did to me" (זה in a relative sense, is qui, for אשׁר, see Ewald, 331): sc., "I eat unleavened bread," or, "I observe this service." This completion of the imperfect sentence follows readily from the context, and the whole verse may be explained from Exodus 12:26-27.

And thou shalt shew thy son {e} in that day, saying, This is done because of that which the LORD did unto me when I came forth out of Egypt.

(e) When you celebrate the feast of unleavened bread.

8. thou shalt show thy son in that day, saying-The establishment of this and the other sacred festivals presented the best opportunities of instructing the young in a knowledge of His gracious doings to their ancestors in Egypt.

13:1-10 In remembrance of the destruction of the first-born of Egypt, both of man and of beast, and the deliverance of the Israelites out of bondage, the first-born males of the Israelites were set apart to the Lord. By this was set before them, that their lives were preserved through the ransom of the atonement, which in due time was to be made for sin. They were also to consider their lives, thus ransomed from death, as now to be consecrated to the service of God. The parents were not to look upon themselves as having any right in their first-born, till they solemnly presented them to God, and allowed his title to them. That which is, by special mercy, spared to us, should be applied to God's honour; at least, some grateful acknowledgment, in works of piety and charity, should be made. The remembrance of their coming out of Egypt must be kept up every year. The day of Christ's resurrection is to be remembered, for in it we were raised up with Christ out of death's house of bondage. The Scripture tells us not expressly what day of the year Christ rose, but it states particularly what day of the week it was; as the more valuable deliverance, it should be remembered weekly. The Israelites must keep the feast of unleavened bread. Under the gospel, we must not only remember Christ, but observe his holy supper. Do this in remembrance of him. Also care must be taken to teach children the knowledge of God. Here is an old law for catechising. It is of great use to acquaint children betimes with the histories of the Bible. And those who have God's law in their heart should have it in their mouth, and often speak of it, to affect themselves, and to teach others.