The Passover

Let the children of Israel keep the Passover at its regular time.
Numbers 9:2

1)1Co 5:7 Take away, then, the old leaven, so that you may be a new mass, even as you are without leaven. For Christ has been put to death as our Passover.
1Co 5:8 Let us then keep the feast, not with old leaven, and not with the leaven of evil thoughts and acts, but with the unleavened bread of true thoughts and right feelings.

References
11Co 5:7 Take away, then, the old leaven, so that you may be a new mass, even as you are without leaven. For Christ has been put to death as our Passover.
1Co 5:8 Let us then keep the feast, not with old leaven, and not with the leaven of evil thoughts and acts, but with the unleavened bread of true thoughts and right feelings.

We Must Separate Ourselves From Those Who Reject The Atonement Of Jesus Christ

Give orders to the children of Israel to put outside the tent-circle every leper, and anyone who has any sort of flow from his body, and anyone who is unclean from the touch of the dead;
Numbers 5:2

We must separate ourselves from those who reject Jesus Christ as the head of The Church in all things.
They have a morally polluted mind, because they have let sin reign in it, and must be separated out of our midst.