Verse 12 tells us that, having considered that suffering is often enduring discipline, we should strengthen ourselves and keep walking with the Lord. Here in Texas we might say “Cowboy up and get back to it”. These are exhortations. He has taught doctrine. Now he teaches how to live out that doctrine.
The language in verses 12 and 13 are poetic. He says to lift your drooping hands, strengthen your weak knees and make straight paths for your feet. All of these are ways of saying do not give in to fear, be strong and stand firm. There might also be an allusion here to Isaiah 35:3-4. That says:
Strengthen the weak hands
and make firm the feeble knees
say to those who have anxious thoughts
be strong, fear not!
Behold, your God
will come with vengeance
with the power of the recompense of God
He will come and save you.
In these verses, the writer gives us some specifics to work for. First he tells us to strive for peace with everyone. It is amazing how much space in the New Testament is devoted to telling Christians to get along with each other. Jesus started it off by praying for the disciples. In John 17:10-11, he prayed that the disciples would be one as he and the Father were one. Paul rebuked the Corinthian church, telling them to have no divisions but to be united in the same mind and same judgment. (1 Corinthians 1:10). Sadly, they did not accomplish this. Clement wrote them years later and again urged them to be united. He said they had envy, strife and sedition. (1 Clement III) Ephesians 4:3 tells us to maintain the unity of the Spirit in the bond of peace. So, we need to make peace in the church, peace with our brothers and sisters in Christ.
We are also to strive for holiness. We do not assume that we make a public profession of Christ and are done. No, we continually work to be holy. We pray and ask for strength, for guidance and conviction from the Holy Spirit. Then we act on that. When we see part of our life that does not conform to the word of God, we change it.
I know the pursuit of holiness is hard in our time. The level of behavior that is perfectly acceptable is horrible. Do not strive to be good as defined by your culture, but by the Bible. A book that drives this point home is Holiness by J. C. Ryle. Another good book is The Pursuit of Holiness by Jerry Bridges.
You should realize that it has always been God’s intention to create a people for himself that are holy. Holy means set apart to God and reflecting his character. In Leviticus 11:44, God instructed the Israelites “consecrate your selves therefore and be holy for I am holy”. Peter reflected this in 1 Peter 1:15, where he says “but as he who called you is holy, you also be holy in all our conduct, sine it is written you shall be holy for I am holy. Believers who reflect God’s holy character honor God. Those who claim to believe but are not holy defame his name.
Verse 15 tells us to see to it that no one fails to obtain the grace of God. We are to watch out for those in our fellowship to make sure their confession is genuine. One way we do that is by constantly preaching the gospel. We do not water it down. We do not tell people they can be saved apart from it.
We are also to see to it that no root of bitterness springs up and causes trouble, because many are defiled by it. This bitterness is not just an unhappy person. It has to do with apostasy, or turning away from God.
This is an allusion to Deuteronomy 29:18. (Remember, this is a book written to Jewish Christians using Old Testament references.) In that verse, Moses said Beware lest there be among you a man or woman or clan or tribe whose heart is turning away today from the Lord our God to go and serve the gods of those nations. Beware lest there be among you a root bearing poisonous and bitter fruit...” In this context, the bitter root is the desire to forsake God for idols. If such a person stays in the fellowship, he defiles it. The Jewish member of the congregation reading this letter would recognize the reference, and recognize it applied to them if they were thinking of abandoning Christ for Judaism. In the same way, people today who are bitter spread their bitterness and defile the fellowship.
Verse 16 tells us that no one is to be sexually immoral in the fellowship. Remember 1 Corinthians 5, where Paul rebuked the Corinthian church for tolerating a man who “has his father’s wife”. A person who has fallen into immorality has to be rebuked so that he or she will repent and be restored. If they do not repent, they must be removed from the fellowship.