"But thanks be to God, who always leads us in His triumph in Christ, and manifests through us the sweet aroma of the knowledge of Him in every place. For we are a fragrance of Christ to God among those who are being saved and among those who are perishing; to the one an aroma from death to death, to the other an aroma from life to life."
The context of Paul's teaching focuses on the Triumph, when the returned Roman army would parade through the city, accepting the accolades of the populace. Interwoven throughout the parade was the burning of incense, as well as masses of flowers. These would be crushed under the horses' hooves, releasing their fragrance. So, the visual experience was enhanced by the scents and aromatic additions of the multitude lining the way.
With such a backdrop, Paul teaches that our salvation is also a triumph, too... as we identify with the victorious Savior and Lord in His conquering of sin, Satan, and the tomb through His atoning crucifixion, burial, resurrection and ascension. Moreover, our knowledge of Him actually manifests a spiritual aroma, well-pleasing to God, which is detected by both saved and lost folk.
As our senses are trained in the discernment of spiritual things, we become more and more sensitive to the "sweet aroma of the knowledge of Christ" in fellow believers. There is a spiritual bond on a level real, yet difficult to describe. It is a kinship of spirit, an underlying commonality witnessed to by the Holy Spirit in each believer. Each and every believer, being indwelt by the Holy Spirit of the living God, manifests the fragrance of Christ, to a greater or lesser degree.
And other Christians are not the only ones who "pick up on" this spiritual reality... "those who are perishing," as Paul phrases it, also sense His fragrance. Yet, for them, it is not an appealing aroma. It is as the stench of death... an unspoken awareness that the God-shaped vacuum in their lives is empty. It is a silent sermon of judgment, creating animosity and discomfort. Could this explain why, upon meeting some unbelievers for the first time, there is an instant dislike on their part? Depending on how strongly the Lord Jesus' scent is manifest, this is a very real possibility. It is an aspect of spiritual warfare that we do not often take into account.
May God grant grace that we will ever, always, and in every place, live fragrant lives of love, to the glory of our Lord Jesus.