This parable is not only applied to the kingdom of heaven, it is also applied to the kingdom of God. It has dual application, then. The parable of the kingdom of heaven show us what will happen as the antichrist’s kingdom spreads throughout the world before the coming of Jesus. The parable of the kingdom of God show us what will happen to Christianity as we near the coming of Jesus.

The kingdom of heaven like a grain of mustard seed

A grain of mustard seed is likened to faith in Matt 17:20; Lk 17:6. This prompts expositors to teach that this parable is about the spread of Christianity throughout the world to become as the greatest tree. They teach that we, through the preaching of the gospel, essentially bring in the kingdom. This is the teaching of amillenialists [those who believe that Jesus is ruling spiritually now and that his kingdom is spreading to cover the earth, eventually converting every soul].

However, they ignore the other types in the parable and other cross-references about the times before the coming of the Lord and so they misinterpret the parable. Look at the associations first.

This parable cannot be about faith in the Lord Jesus Christ spreading throughout the world because:

This faith is sown in the world and yields a huge kingdom in which there are devils.

The world has never desired Jesus Christ to be its king [Jn 1:9-10, Jas 4:4].

Jesus was concerned whether he would find faith on the earth when he comes [Lk 18:8]

This kingdom is like Nebuchadnezzar’s kingdom that spread into a great tree [Dan 4]. It is also like the spread of Pharaoh’s kingdom in Eze 31:1-18. Nebuchadnezzar and Pharaoh are two of the greatest types of the antichrist in the Bible. The kingdom of heaven, therefore, instead of spreading the faith of Jesus Christ, becomes a religious monstrosity [Rev 18:1-4] with the antichrist in charge [2 Thes 2:3-4, 9-10].

The kingdom of God like a grain of mustard seed

Now that we have the associations and the interpretation down by cross-referencing scripture with scripture, we can understand the application of this parable to the kingdom of God.

It shows us that as we near the coming of the Lord, Christianity goes into apostasy [2 Thes 2:3]. This is evidenced in several ways. The number of "professing" Christians is huge by comparison to the number of truly saved believers. The largest single "church" of professing Christians (Roman Catholicism) gives "heed to seducing spirits and doctrines of devils," (1 Tim 4:1-3), typified by the birds in the tree. The proliferation of modern translations has destroyed faith in the words of God for the majority of professing Christians (Rom 10:17). Their faith is in words corrupted by the devil. So, the tree is large but it is filled with devils, like the purpose driven church movement or the charismatic movement.