Generally, when Christians refer to the harvest at the end of the age (Rev 14:15-20), we often think of a great influx of souls coming to Christ from the world. However, scripture and the Early Church tells us there first has to come a harvest within us, before the harvest of the nations.
All harvest starts with seed. If you want a crop of tomatoes you plant tomato seeds, likewise if you want to make bread, you sow grain to harvest wheat. There are many parables in scripture that use agriculture and farming terms, but when we understand that every parable is an earthly story with a heavenly meaning, (1) we see that God isn’t trying to teach us how to get a good crop in the natural. Jesus tells his disciples in Luke 8:11 that the seed is the Word of God. Bearing this in mind, we can see that scripture is teaching us how to sow the Word of God in the heart of man, just as Jesus talks about in the parable of the seed and the sower in Matthew 13. If the seed is spiritual (symbolic), that must mean the harvest that comes from sowing the Word of God is spiritual also. The Apostle Paul tells us that there is a sowing to the flesh, and a sowing to the spirit bringing everlasting life, again confirming it is not about sowing seed in the natural:
Do not be deceived, God is not mocked; for whatever a man sows, that he will also reap. For he who sows to his flesh will of the flesh reap corruption, but he who sows to the Spirit will of the Spirit reap everlasting life. (Galatians 6:7-8)

Origen, a third-century Early Church Father, wrote the following, showing us the agreement with Scripture and the Early Church understanding, that what God plants is a spiritual seed. God uproots vices and plants virtue in the soul of those who are faithful in His word.
What is it that God plants? Moses says that “God planted paradise” (Gen 2:8). But God is planting now as well, and he is planting daily in the souls of the faithful. For in the soul from which he removes anger he plants gentleness, and in the soul from which he removes pride, he plants humility. (2)

When writing to the Church of Galatia Apostle Paul called the Church his (spiritual) children, in whom he was laboring to form, or birth, Christ in (Galatians 4:19). In Hebrew, the word for seed also means sperm (3). So, Paul was saying that he has the spiritual seed/sperm from God to impregnate the Church and cause Christ to be birthed within them. To birth something is akin with bringing forth a harvest. Christ means “anointed” (4) and in Acts 10:38 the Word says Jesus was anointed with the Holy Spirit. The evidence of the Holy Spirit is the fruit of the spirit as found in Galatians 5:22-23, Ephesians 5:9, Hebrews 13:15. So, the harvest of the Word of God is the fruit of the spirit, or the nature of Christ. Because Paul had the nature of Christ within him, through his teachings and walking as Christ did, he was able to impart those fruits into his own disciples which was forming Christ’s nature within them. From the beginning of the formation of the Church, the pattern was set that Apostles would be required until we come into perfection in Christ’s nature (Ephesians 4:11-16). Notice how Paul was endowed with the fruit of the spirit, but it wasn’t just for him to keep and not pass on. Jesus gave the commission to the Disciples in Mark 16:18-20 to make disciples of all men, baptizing them in the Holy Spirit and teaching them all that was commanded of them.
Here Mathetes confirms that the Tree of Life are those bearing the fruits of the spirit:
When you have read and carefully listened to these things, you shall know what God bestows on such as rightly love Him, being made [as ye are] a paradise of delight, presenting in yourselves a tree bearing all kinds of produce and flourishing well, being adorned with various fruits. For in this place the tree of knowledge and the tree of life have been planted; but it is not the tree of knowledge that destroys — it is disobedience that proves destructive. Nor truly are those words without significance which are written, how God from the beginning planted the tree of life in the midst of paradise, revealing through knowledge the way to life, and when those who were first formed did not use this [knowledge] properly, they were, through the fraud of the Serpent, stripped naked. For neither can life exist without knowledge, nor is knowledge secure without life. Wherefore both were planted close together. The Apostle, perceiving the force [of this conjunction], and blaming that knowledge which, without true doctrine, is admitted to influence life, declares, “Knowledge puffeth up, but love edifieth.” For he who thinks he knows anything without true knowledge, and such as is witnessed to by life, knows nothing, but is deceived by the Serpent, as not loving life. But he who combines knowledge with fear, and seeks after life, plants in hope, looking for fruit. (5)

Mathetes not only says that the Tree of Life is within us, but that obedience to true knowledge or doctrine is what brings life. We discussed earlier how the seed is the Word of God, so here true knowledge and doctrine is the seed imparted by the Apostles of the church. The fruit is the harvest of that true seed.
Origen writes the following, expounding further on the harvest at the end of the age and who God uses to remove the vices of the souls.
And at the end of things, which is called “the consummation of the age, ”there will of necessity be a harvest, in order that the angels of God who have been appointed for this work may gather up the bad opinions that have grown upon the soul, and overturning them may give them over to fire which is said to burn, that they may be consumed. And so the angels and servants of the Word will gather from all the kingdom of Christ all things that cause a stumbling-block to souls and reasonings that create iniquity, which they will scatter and cast into the burning furnace of fire. Then those who become conscious that they have received the seeds of the evil one in themselves, because of their having been asleep, shall wail and, as it were, be angry against themselves; for this is the “gnashing of teeth.” (6)

Origen says the angels and servants of the Word gather in the end-time harvest. In Hebrew, the word for Angel means a messenger of God, a prophet, priest or teacher. (7) In Greek, the word Angel refers to the Bishop of the church (8), also known as the Apostles. And in Amos 3:7-8 scripture tells us that God’s servants are the prophets. So, we can see here that an angel of God is not just referring to an ethereal being with wings, that lives in the heavens; rather an angel is an Apostle or Prophet chosen by God to bring a message to His people. What are these Apostles and Prophets gathering? Origen tells us that they are gathering up the reasonings within us that create iniquity, which in Hebrew means sin (9) and consuming them by fire. In Hebrew, fire speaks of the mysteries and secrets of the Word of God. (10) and in 1 Corinthians 4:1 the Apostle Paul describes the ministry of the Apostles as the stewards of the mysteries of God. So the Apostles and Prophets are sent to remove the sin or carnal nature (1 Corinthians 3:3) from within us by the mysteries they are releasing. Earlier, we read from Origen that God plants virtue in place of vice and here he writes that the Angels and Prophets remove sin, so that must mean that these angels and prophets also help to plant virtue in place of the vices in our soul.
For further evidence that the harvest at the end of the age are the virtues (character) of Christ in us, let us read on. Origen writes the following:
And perhaps everything that is perceivable by the senses, right up to heaven itself and what is in it, are fields white for the harvest, waiting for those who lift up their eyes (Jn 4:35) . . . “Lift up your eyes, and see how the fields are already white for harvest” Jn 4:35). The WORD that is present to the disciples is encouraging the hearers to lift up their eyes towards the fields of the scriptures and to the fields of the WORD in each being in order to see the whiteness and the brilliance of the light of the truth which is everywhere. (11)
In another place he writes,
Perhaps each individual virtue is a kingdom of heaven, and all of them together are the kingdom of heaven. According to this, whoever lives a virtuous life is already in the kingdom of heaven; and the words: “Repent, for the kingdom of heaven is at hand” (Mt 3:2; 4: 17) do not refer to time but to deeds and the inner disposition that goes with them. For Christ, who is every virtue, has completed his coming and speaks; consequently, the kingdom of God is within his disciples, and not “here” or “there” (cf. Lk 17:21). (12)

Following the thread in these excerpts by Origen, we can see that the fields white for harvest are not only speaking of the scripture, but the fields of the Word (Christ) within each true believer. He shares that heaven itself are the fields white for harvest which symbolically refers to heavenly mindsets and virtues within us.
Just as a seed or grain in the natural, when watered and nurtured, brings forth a harvest of plants or wheat, so too does the spiritual seed when watered with the Word of true doctrine, and nurtured in our souls, brings forth a spiritual tree- the Tree of Life. The harvest we should be striving for and expecting through diligent labor, is the fruit of the spirit, or the virtues of Christ within us. This then divinely empowers us to form Christ in others, to gather in the harvest in them, which is our commission in following the pattern of Christ. Amen.
References:
- Thayer’s Dictionary: ‘Parable’ (G3850)
- Origen, Homily on Joshua, Homily 13
- Brown Driver Briggs Dictionary: ‘Seed’ (H2233)
- Thayer’s Bible Dictionary: ‘Christ’ (G5547)
- Mathetes, Epistle to Diognetus Ch XII
- Origen, Commentary on The Gospel of Matthew, Book X
- Strong’s Bible Dictionary: ‘angel’ (H4397)
- Complete Word Study Dictionary: ‘angel’ (G32)
- Strong’s Bible Dictionary: ‘Iniquity’ (H5771)
- Ancient Hebrew Lexicon Bible Dictionary: ‘Fire’ (H3857)
- Origen, Commentary on John, Book XIII
- Origen, Commentary on the Gospel of Matthew, Book XII
All scripture references from The Holy Bible: New King James Version: NKJV. Thomas Nelson, 2010, unless stated otherwise,