To understand the meaning of the "therefore" in scripture, you have to consider what it is "there for". If we keep in mind this word is used as a means of joining supporting thought together, we will then be encouraged to look at what precedes the therefore to see what it is there for. In this passage, Paul has just finished telling the believers at Philippi they need to live worthy of Christ's gospel. The gospel is just another way of saying the good news Christ brings into the lives of those he touches. It isn't just the set of scripture we have which we call our Bible, but the Words of God which set at liberty the bound spirit and distressed soul. In essence, Paul is reminding us of the importance of being "united" in thought, purpose, and action. We aren't to have our own little way of doing things while others have their own - but are to live in harmony with each other, learning from one another, and drawing closer and closer to Christ in the process. Unity is more than having a few things in common, but it is a mindset and determination to be consistently living in a manner which honors the other people around us. Paul knew there would be a continual struggle to remain faithful to the gospel, especially in the face of persecution, conflicting opinion, and beliefs which concluded their faith to be in vain. Most of the time we don't need reminders that we have enemies - it is pretty apparent whenever we try to take even one step forward because their opposition is ever-present. In the face of all this, we are to stand strong and there is no other way to do so than to be focused on the unity of faith we are to maintain. At this revelation, Paul enters with the "therefore" - selfish purpose will destroy this unity, so be sure to guard against it.
Therefore, if there is any encouragement in Christ, any comfort in love, any sharing in the Spirit, any sympathy, complete my joy by thinking the same way, having the same love, being united, and agreeing with each other. Don’t do anything for selfish purposes, but with humility think of others as better than yourselves. Instead of each person watching out for their own good, watch out for what is better for others. (Philippians 2:1-4 CEB)
It is as though Paul is asking if there is any way we can stand with each other in such a way so as to bolster one another's confidence to stand strong in midst of the hard times we will face. It is this "standing with" which Paul has in mind as the means by which many will be able to not only endure the trials they will face, but come out victorious on the other side of them. We share the same Spirit - the Spirit of Christ - that makes us "kin" to one another. "Kin" is supposed to look out for "kin". I know that seems a little elementary, but in a world which really focuses more on "what's in it for me" than "what can I do for another to bless them" this thought is not really as well understood as some may think.
Working together with one heart, mind, and purpose. The heart is the seat of our emotions, so if we can get the emotional balance to not be so easily swayed by this influence or that one, then we might stand a better chance of being united in our purpose. The mind is the place of thought or consideration. It can be the beginning of many a right action, but also many a selfish belief or purpose. If we get the emotions under control and the mind aligned with God's mind, then the purpose we begin to operate within will be solid. To this end, Paul asks us to consider our heart, mind, and allow our purpose to begin to be united under the banner of Christ's love and grace.
It takes some doing to make this "shift" in our way of thinking and operating in life. It is easy to be swayed by the most powerful of emotions - often discounting rational thought in pursuit of what feels "better" or "best" to us at the moment. This is why we cannot rely upon how we feel when it comes to taking steps toward or away from anything in life. If we relied solely upon our emotions, we'd be going a hundred different directions each week because they are up one day and down the next. While emotions lend the "stuff" to life which helps us to really experience the depth of joy and excitement, or the tranquility of true peace, we cannot count on our emotions to always steer us in the right direction.
Herein comes the help we lend to each other in relationship - we help to restore balance when emotion has been allowed to captivate our thoughts in any irrational or unreasonable way. We act as "check and balance" for one another. In so doing, we are helping to maintain the unity which will drive us forward as a strong force to be reckoned with! If we want strength it comes in more than just numbers! Numbers of people all together is just a crowd. Numbers of people united in purpose is an army to be reckoned with! I don't know about you, but I want to walk closer to Jesus because of the people I am united with in my daily life. I want to enjoy a greater sense of peace in my life because of the strength this unity produces. I want to have a stability in my thoughts which produce consistency in my actions. In essence, I want to know others are watching out for me, and I need them to know I am watching out for them! Just sayin!