Mt 13:35 That it might be fulfilled which was spoken by the prophet, saying, I will open my mouth in parables; I will utter things which have been kept secret from the foundation of the world.
Jesus spoke in parables.
Mr 4:11 And he said unto them, Unto you (obedient disciples) it is given to know the mystery of the kingdom of God: but unto them that are without, all these things are done in parables:
Mr 4:12 That seeing they may see, and not perceive; and hearing they may hear, and not understand; lest at any time they should be converted, and their sins should be forgiven them.
Mr 4:34 But without a parable spake He (Jesus) not unto them: and when they were alone, he expounded all things to his disciples.
So here we see that Jesus spiritualized everything when speaking to those who were immature or unbelievers, 1 Cor 14:23. It can also be seen here that He demonstrated the Gift of speaking in Tongues and the interpretation of the gift of Tongues.
God does not speak to Christians as He does to unbelievers. If a Christian does not understand a message that Jesus spoke in public, He explains/interprets it to them privately.
Spiritualizing things is the way that God conceals truths from those that He does not want to understand.
Mt 13:14 And in them is fulfilled the prophecy of Esaias, which saith, By hearing ye shall hear, and shall not understand; and seeing ye shall see, and shall not perceive:
Esaias (Isaiah) was speaking to God’s unclean people.
Isaiahs commission was to –
Isa 6:10 Make the heart of this people fat, and make their ears heavy, and shut their eyes; lest they see with their eyes, and hear with their ears, and understand with their heart, and convert, and be healed.
God did not want His people (Judah and Jerusalem) to be healed because they had provoked Him with their speech and actions, Isaiah 3:8.
God takes Isaiah’s sin away in 6:6 and 7, and then sends him to speak to “Unclean” people until they are “desolate”, verse 11. Daniel 9:27 shows that God makes something desolate because of sin.
If they are desolate/willfully sinful, they will be judged (Heb 10:26-27) and directed towards repentance, 1 Cor 11:32.
If God was going to shut their eyes with Isaiah’s messages, then they had to have been open previously.
He shuts their eyes and ears as they hear but are not given the ability to understand Isaiah’s messages.
God gives a person the interpretation of a particular parable or He conceals it from them.
Mr 4:12 That seeing they may see, and not perceive; and hearing they may hear, and not understand; lest at any time they should be converted, and their sins should be forgiven them.
The reason for speaking in parables or tongues is to conceal the messages from unbelievers. This includes believers who provoke God through their sin, 1 Cor 14:23.
Here in Isaiah, we see that the understanding that believers possess can be taken away, Matt 13:12 and 25:29.
Mt 25:29 For unto every one that hath shall be given, and he shall have abundance: but from him that hath not shall be taken away even that which he hath.
The reason that God spiritualizes messages is to conceal them. To interpret an intentionally spiritualized message as if it was literal is to interpret it in its intentionally misleading manner.