Why does the LORD allow false prophets?

One question I'm asked a lot is "Why does the Lord allow false teachers?" I ask myself that question a lot! Another question related to it is, "Why do false teachers prosper?" We're not alone in asking this. Job, Jeremiah, and David all asked the same thing. (Job 21:7, Jeremiah 12:1, Psalm 94:3). You and I are in good company!  I think of Joyce Meyer and Joel Osteen and other false teachers especially on the African continent, who live high off the hog and rake in millions of dollars, and it grieves me to see the sheep led astray and the false teachers enjoying a comfortable life filled with amenities, acclaim, and comfort. So...why??

He is testing us.

If a prophet or a dreamer of dreams arises among you and gives you a sign or a wonder, and the sign or the wonder comes true, concerning which he spoke to you, saying, ‘Let us go after other gods (whom you have not known) and let us serve them,’ you shall not listen to the words of that prophet or that dreamer of dreams; for the LORD your God is testing you to find out if you love the LORD your God with all your heart and with all your soul. You shall follow the LORD your God and fear Him; and you shall keep His commandments, listen to His voice, serve Him, and cling to Him. But that prophet or that dreamer of dreams shall be put to death, because he has counseled rebellion against the LORD your God who brought you from the land of Egypt and redeemed you from the house of slavery, to seduce you from the way in which the LORD your God commanded you to walk. So you shall purge the evil from among you. (Deuteronomy 13:1-5).

Walvoord's The Bible Knowledge Commentary says, "The need to maintain national purity was emphasized by Moses, for the command, 'You must purge the evil,' occurs nine times (13:5; 17:7, 12; 19:19; 21:21; 22:21–22, 24; 24:7)."

In their Commentary Critical and Explanatory on the Whole Bible, Jamieson, Fausset & Brown title the warning about following false prophets section of Deuteronomy, "Enticement to Idolatry". One can only be enticed, (or seduced as Paul said in 2 Timothy 3:13) if there is some aspect of your (my) flesh that responds to enticement. It's our job to vigilantly slay pockets of sin in us so that the flesh will not seek fulfillment through idols, whatever they may be.

The Commentary says,

If there arise among you a prophet—The special counsels which follow arose out of the general precept contained in De 12:32; and the purport of them is, that every attempt to seduce others from the course of duty which that divine standard of faith and worship prescribes must not only be strenuously resisted, but the seducer punished by the law of the land. This is exemplified in three cases of enticement to idolatry

In the Old Testament Law, false prophets were stoned to death.

In Walvoord's The Bible Knowledge Commentary, we read,

The Israelites were to view each solicitation to idolatry as a test of their love for the LORD. Though there was always the danger that they might succumb to a temptation, with each successful resistance to sin their faith in and love for Him would grow stronger (cf. James 1:2–4). They were to love … follow … revere … obey … serve, and hold fast to Him (cf. Deut. 10:20; 11:22; 30:20). The death penalty for a false prophet was appropriate for if he would successfully seduce people into idolatry he would bring them under God’s judgment (cf. 7:26). Killing a false prophet was a way to purge the evil from Israel

Matthew Henry explains about the testing.

Not only thou shalt not do the thing he tempts thee to, but thou shalt not so much as patiently hear the temptation, but reject it with the utmost disdain and detestation. Such a suggestion as this is not to be so much as parleyed with, but the ear must be stopped against it. "Get thee behind me, Satan." Some temptations are so grossly vile that they will not bear a debate, nor may we so much as give them the hearing.

The need to purge evil hasn't changed. In this Church age, too many people deem it 'tolerant' or 'merciful' or 'non-judgmental' to entertain false teachers, to give the false prophets a hearing, debate them, or to stay quiet about them. We must reject false teachers with the "utmost disdain." In today's time we don't stone the false prophets to death, but we do practice church discipline over the grossly sinning unrepentant ones who claim Christ, we excommunicate them so they will not seduce others, and we mark the false teachers and we avoid the false teachers and we do not receive them into our house, and more.

If we fall for false doctrine put out buy a false teacher, it means we have been seduced. If we've been seduced, it means we have fed the flesh in some form of sinful lust it had wanted. If we succumb to satisfying he flesh, it means we have not loved the Lord with all our heart, mind, strength, and soul, back up to Deuteronomy. Therefore we can see how the LORD tests us. It's our job in Him to stay as pure as possible so we do not follow a false teacher who brings a substitute for God in the form of doctrine which appeals to the flesh. We must not be enticed to idolatry.

The Lord is testing us.

Examine yourselves, to see whether you are in the faith. Test yourselves. Or do you not realize this about yourselves, that Jesus Christ is in you?—unless indeed you fail to meet the test! (2 Corinthians 13:5).