Colossians 3:15-16

And let the peace (soul harmony which comes) from Christ rule (act as umpire continually) in your hearts [deciding and settling with finality all questions that arise in your minds, in that peaceful state] to which as [members of Christ’s] one body you were also called [to live]. And be thankful (appreciative), [giving praise to God always]. Colossians 3:15

We are told that we are to let Jesus’ peace settle all of our questions and Jesus’ peace is absolutely settled. He has already been raised up from the grave, death no longer has any hold on Him and He has been returned to the glorious state of existence that He had with God before He came to the earth to be sacrificed. His peace in Who He is and what He has is what is to settle all of our questions. If Jesus has it, so do we. How can the head possess something that its body does not? So if you have any questions think about Jesus and what He has or is and then relax, because that is what you have as well.

Let the word [spoken by] Christ (the Messiah) have its home [in your hearts and minds] and dwell in you in [all its] richness, as you teach and admonish and train one another in all insight and intelligence and wisdom [in spiritual things, and as you sing] psalms and hymns and spiritual songs, making melody to God with [His] grace in your hearts. Colossians 3:16

Jesus and the Word are One. In the beginning was the Word and the Word was God and the Word was with God and it became flesh and dwelt amongst us. So our peace is that the Word is in our hearts and it will never leave us. In fact it cannot ever leave us. The Word will teach us all things. It will settle every doubt, fear, and question that we will ever have. The Word knows what it is like to be us and it has already overcome any weapon that has been formed against us. The Word is Victorious and we are one with it. 

Faith comes for us by hearing the Truth and the Truth is that we cannot fall short in any area of our lives. For us to fail would mean that our Head, Who is Jesus, Who is God, Who is the Word, had failed.

But thanks be to God, Who in Christ always leads us in triumph [as trophies of Christ's victory] and through us spreads and makes evident the fragrance of the knowledge of God everywhere, 2 Corinthians 2:14

And I am convinced and sure of this very thing, that He Who began a good work in you will continue until the day of Jesus Christ [right up to the time of His return], developing [that good work] and perfecting and bringing it to full completion in you. Philippians 1:6

I have strength for all things in Christ Who empowers me [I am ready for anything and equal to anything through Him Who infuses inner strength into me; I am self-sufficient in Christ's sufficiency]. Philippians 4:13

Whenever we are told or believe that we have to do something our peace is that it is never just us who has to do it, it is always Christ in us doing everything. We can do nothing on our own, ever. It is always Christ in us.