Whoever thus serves Christ is acceptable to God and approved by men.  So then let us pursue what makes for peace and for mutual upbuilding. (ESV)
Paul has given instruction in the previous verse about how we are to treat one another in the body of Christ. We are not to turn our involvement in the kingdom of God into a squabble about who can eat certain kinds of foods and who cannot. Rather, our focus should be on pursuing righteousness, walking in peace, and choosing to have joy in all circumstances with the help of the Holy Spirit.
The ones who walk obediently like this, with their eyes on Christ Jesus, will not only be acceptable to God, but also will be approved by men. We understand why our obedience would be acceptable to God, but what does it mean that we will be approved by men? After all, shouldn't God's approval be all that we need?
This idea of being approved by men speaks to the fact that the world of non-believers is constantly examining the Church. They want to see if the faith we proclaim is actually real. If they see us squabbling over petty things they will see us as hypocrites. Being approved by men speaks of our godly testimony that cannot be refuted because our life backs it up.
From a practical standpoint, we should be pursuing that which makes for peace and builds each other up. As we can see, this is not only for the benefit of our right standing with God, but this pursuit of peace and mutual upbuilding is so that the world can see how we behave and they can glorify our Father in Heaven. Our testimony is gravely important.
In your encounters with other believers are you pursuing peace? Do you strive to build others up? Or are you too busy seeking your own way? Do you have God's approval? Man's?