Jeremiah 10:1-5 reveals a principle that we need to consider in terms of Halloween. The context is the heathen practice of idolatry. In this sense, it is ironic that Halloween comes primarily from the Celts, descendants of the Israelites.
God commands us not to learn the way of the Gentiles, the nations who do not have the revelation of God. The Israelites were different from all the nations chiefly because God had revealed Himself to them and given them His law (Deuteronomy 4:5-8; Amos 3:1-2). The Gentiles invented their own futile, meaningless ways of worship because they did not have the truth.
This is the first reason why we should not keep Halloween. It adds nothing good, that is, nothing of God or godliness, to our character. Being devoid of God's truth, it is simply worthless and a waste of time.
Richard T. Ritenbaugh