I believe Paul gives us very clear instructions. 1 Whatever happens, my dear brothers and sisters, Rejoice in the Lord. I never get tired of telling you these things, and I do it to safeguard your Faith {Phil 3:1} To rejoice in the Lord does a great many things. Even the fact that we rejoice in the Lord shows Faith. We express our Trust and Hope in Christ. Some synonyms for rejoice: celebrate; triumph. Our Faith in Jesus is not only safeguarded but, we reaffirm and build up our Faith as we Rejoice; Celebrate; we Triumph in Christ Jesus. In verses 3 and 9 we see one of the most powerful reasons. 3 For we who worship by the Spirit of God are the ones who are truly circumcised. We rely on what Christ Jesus has done for us. We put no confidence in human effort,..{Phil 3:3}... I no longer count on my own righteousness through obeying the law; rather, I become righteous through faith in Christ. For God’s way of making us right with Himself depends on Faith. {Phil 3:9} “...I become Righteous through Faith in Christ. For God’s way of making us right with Himself depends on Faith.” Again, our Faith is safeguarded as we Rejoice in the Lord.

Let me go at this from a different angle. What makes Rejoicing in the Lord effective, in building up and safeguarding our Faith? When people we know and love have been away from us for a time. When they return to us what do we do? We rejoice that we are together once more. That part of our heart that we gave that person, has returned to us. The act of rejoicing reaffirms our love and the importance the relationship means to us.
As we share about the things we have been doing, of the wisdom we may have gained since we have been apart. In sharing that wisdom we edify one another.

Rejoice in the Lord always. I will say it again: Rejoice! {Phil 4:4} NIV
Always be Joyful in the Lord! I'll say it again: Be Joyful! GWT Our lives are full of choices. We all make good and bad ones at times. This need not be one of them. Let us Rejoice in the Lord, let us be glad for the Relationship we have with Our Lord, Christ Jesus. When we rejoice, sadness, fear, hopeless, and negative emotions lose their hold on our thoughts and hearts. Our Salvation and Righteousness have been bought and paid for by the Love; the actions of Christ. Yes, I do not believe we can separate the actions of Jesus from Love they are one and the same. At those times when we least feel like rejoicing, they are the times when we must decide to Rejoice the most. For the Sacrifice of Praise is a Powerful tool, one we must never underestimate.