As long as you are in Jesus you will be kept from falling
14 And Enoch also, the seventh from Adam, prophesied of these, saying, Behold, the Lord cometh with ten thousands of his saints,
Enoch was taken, that was an example of the rapture of the church. Being the seventh from Adam is a reference to the church as the number seven is associated repeatedly with a complete work done on God's people. Enoch is the root of the word for Hannukah and it means dedicated, consecrated. There are a lot of people who will say they are Christians, but now many of them are fully consecrated to the Lord. Many sing a song for the Lord to send them where He would send them, but then when they are told by the Lord to go somewhere they won't go. They don't want to give up the job or sell the house or lose their friends, etc. So when the church is raptured then ten thousands of His saints come, a reference to the 144,000 evangelists during the tribulation. The word for ten thousands can be translated as ten thousand times ten thousand, which is 100 million. That is certainly a whole lot more encouraging, but even so, 100 million is less than 2% of the world's population and closer to 1%.
15 To execute judgment upon all, and to convince all that are ungodly among them of all their ungodly deeds which they have ungodly committed, and of all their hard speeches which ungodly sinners have spoken against him.
During the age of grace we are speaking the gospel which is that everyone is a sinner, but you can be saved by the sacrifice that the Lord made. People have felt they have plenty of time to make a decision for Christ. But during the tribulation the clock has run out, people will be forced to make a decision. Also the ungodly deeds will be multiplied, which is why he starts this epistle with multiplied mercy.
16 These are murmurers, complainers, walking after their own lusts; and their mouth speaketh great swelling words, having men's persons in admiration because of advantage.
We call this kind of person a brown nose or yes men. They think the secret to getting ahead is to be the number one fan of the guy in charge. Christians in contrast to these are only concerned with what the Lord says. As long as the Lord says well done thou good and faithful servant then they are happy. Also, we are not looking for an advantage in this present age. We understand this is a brief period of tribulation that we go through before we enter eternity.
17 But, beloved, remember ye the words which were spoken before of the apostles of our Lord Jesus Christ; 18 How that they told you there should be mockers in the last time, who should walk after their own ungodly lusts.
19 These be they who separate themselves, sensual, having not the Spirit.
This has become abundantly clear with social media. The things people say, the mocking, the ungodly lusts, the sensuality, the people who separate themselves from the Bible, from the Church, from Christians. We were warned and we should be encouraged because if you are experiencing this then you must be on the front lines battling the gates of hell.
20 But ye, beloved, building up yourselves on your most holy faith, praying in the Holy Ghost,
In my experience either we are building up our most holy faith or we are being torn down. There is no in between. Think of the Christian life as a marathon race. If you are not moving forward, it isn't just that you are stopped, it is that the rest of the racers are passing you by. To me building yourself up in the faith is done by spending time in the word of God, in fellowship, and in study of the word. However, the application of that is in prayer. Jesus said that they came to the word of God because they thought that was where the life was but the word of God testified of Jesus and they didn't come to Jesus. The word of God testifies to us of Jesus, then we take that word to God in prayer so that we could be filled with Jesus.
21 Keep yourselves in the love of God, looking for the mercy of our Lord Jesus Christ unto eternal life.
Many would say "keep yourself in the word of God" but there are many who are in the word of God but not in the love of God. They are like the church in Ephesus which was good and figuring out who was and who was not a prophet of God but they left their first love. If we are building up our holy faith then we are in the word of God, if we are praying then we are going to the Lord. If we keep ourselves in the love of God, that is a three fold cord. Ruth comes to us, we are in the word of God, we know that a Moabite cannot enter the congregation to the tenth generation. However, we don't judge Ruth, instead we take this word to the Lord in prayer, praying that we would keep ourselves in the love of God. In the love of God we get the word that Ruth is also the widow of an Israelite and the word of God says that we are to raise up seed to our brother who died by taking care of his widow. Now, we are looking to show mercy to people because if we show mercy to them God will show mercy to us. Here is a great opportunity to show Ruth mercy, instead of judging her because she is a Moabite I show her mercy by recognizing that she is the widow of an Israelite.
22 And of some have compassion, making a difference: 23 And others save with fear, pulling them out of the fire; hating even the garment spotted by the flesh.
Boaz had compassion and that made a difference. But with Lot the angels had to pull him out of the fire and only three out of six of the family actually made it out of the fire.
24 Now unto him that is able to keep you from falling, and to present you faultless before the presence of his glory with exceeding joy, 25 To the only wise God our Saviour, be glory and majesty, dominion and power, both now and ever. Amen.
https://www.biblegateway.com/passage/?search=3 John 1&version=KJV
You cannot keep yourself from falling, only Jesus can. That is why everyday we need to go to Jesus and stay in His presence. As long as you are in Jesus you will be kept from falling.