Guard and keep yourselves in the love of God ...

Don't lose heart or grow faint. God knew these days would come. We were forewarned so that we would not be surprised nor alarmed:

They (the Apostles) told you beforehand, In the last days (in the end time) there will be scoffers - who seek to gratify their own unholy desires - following after their own ungodly passions. Jud 1:18-AMP

It is these who are (agitators) setting up distinctions and causing divisions; merely sensual [creatures] - carnal, worldly-minded people - devoid of the (Holy) Spirit and destitute of any higher spiritual life. Jud 1:19-AMP

But you, beloved, build yourselves up [founded] on your most holy faith - make progress, rise like an edifice higher and higher - praying in the Holy Spirit; Jud 1:20-AMP (1Co 14:4; Act 1:4; 8:14-17; 10:44-47; 19:2-6)

Guard and keep yourselves in the love of God; expect and patiently wait for the mercy of our Lord Jesus Christ, the Messiah, [which will bring you] unto life eternal. Jud 1:21-AMP

"Guard and keep yourselves" -

"Building yourselves up" -

"Praying in the Holy Ghost"