Jesus didn’t tell us to kill unbelievers. He told us to be faithful. As mysterious as it is in the OT, God’s judgment often comes through a faithless invading army. So, the immediate context of the parable is Jesus ascending to the Father to receive his kingdom (Lk 19:12) and returning to judge those who reject his royal authority (Lk 19:27) in the form of the Roman army. So, the coming judgment is first a reference to the downfall of Jerusalem in 70 A.D. and not Christ’s second coming.
As he drew near, he saw the city and wept over it, saying, “If this day you only knew what makes for peace–but now it is hidden from your eyes. For the days are coming upon you when your enemies will raise a palisade against you; they will encircle you and hem you in on all sides. They will smash you to the ground and your children within you, and they will not leave one stone upon another within you because you did not recognize the time of your visitation.” (Lk 19:41-44)
"When you see Jerusalem surrounded by armies, know that its desolation is at hand. Then those in Judea must flee to the mountains. Let those within the city escape from it, and let those in the countryside not enter the city, for these days are the time of punishment when all the scriptures are fulfilled. Woe to pregnant women and nursing mothers in those days, for a terrible calamity will come upon the earth and a wrathful judgment upon this people. They will fall by the edge of the sword and be taken as captives to all the Gentiles; and Jerusalem will be trampled underfoot by the Gentiles until the times of the Gentiles are fulfilled. (Lk 21:20-24)
That event was itself a prophetic preview of his Second Coming in glory to judge all nations at the end of time, which was also part of the earlier parable.