Verse 21 says to keep yourselves in the love of God. Surround yourself with God's love. When we surround ourselves with God's love it is harder for the enemy to work in our lives. For God's love, perfect love, casts out all fear. There will be no need to be fearful or anxious for anything.
Verse 20 says we can build ourselves up on our faith, praying in the Holy Ghost. Thank God for the Holy Ghost, our Comforter and Guide. The One who helps us pray. The One who convicts when we are wrong and helps us to be restored when we repent. Then Verse 24 says that God is able to keep us from falling and present us faultless before the presence of His glory with exceeding joy.
The only joy, true joy is found in Jesus. In trusting Him. The joy of the Lord is our strength. He is the only one who can keep us from falling in this evil time, if we allow Him to. Do you want to make it all the way victoriously? Then trust God to see you through. He will never fail you.