This verse is part of Jesus' explanation of the Parable of the Wheat and the Tares (weeds), found in Matthew 13:24-30 and 36-43. Let's break down the meaning of Matthew 13:39 in that context:

"The enemy who sowed them is the devil."
Jesus identifies the "enemy" who sowed the tares (weeds) among the wheat as the devil (Satan). The tares represent people who appear to be followers of Christ but are actually not genuine believers or are actively working against God's purposes. The devil is the one who introduces these false believers or influences people to turn away from true faith.

"The harvest is the end of the age."
The "harvest" symbolizes the final judgment at the end of the current era or "age." This is the time when God will separate the righteous (the wheat) from the wicked (the tares).

"And the reapers are angels."
The "reapers" are the angels, who will be responsible for carrying out the separation and judgment at the end of the age. They will gather the righteous and the wicked according to God's instructions.

In Summary:

The verse is saying that the devil is responsible for introducing evil and false believers into the world. At the end of the world, there will be a final judgement where angels, acting as God's reapers, will separate the truly righteous from those who only appeared to be so.

Broader Implications:

Discernment: The parable and this verse encourage believers to be discerning and not be naive about the presence of evil in the world and even within the church.
Patience: It also suggests patience, as God allows both good and evil to coexist for a time until the final judgment.
Judgment: It emphasizes the reality of a final judgment where everyone will be held accountable for their actions and beliefs.
God's Sovereignty: Ultimately, it highlights God's sovereignty over all creation and His ultimate triumph over evil.

In essence, this verse provides a glimpse into the spiritual battle between good and evil and the ultimate outcome of that battle at the end of time.