As a kid growing up in the church, it used to bother me when preachers would refer to Christians as “aliens.” I had never seen a green, monster-like creature with spaghetti antennas on 
his head at church! Why must they insist on using that word?
Such is the way that God refers to His people in the Bible! The Lord pleads with His people to “abstain from fleshly lusts” (1 Pet. 2:11) and bases that exhortation upon Christians being “aliens and strangers” (NASB) or “sojourners and pilgrims” (NKJV). The first word denotes one who is dwelling in a foreign country, and the second word denotes one who is staying temporarily away from home.
In every sense of the word, Christians are aliens. We are living on this earth, but it is a “foreign country” to the “citizenship” that we have “in heaven” (Phil. 3:20). And, thankfully, we are merely passing through, on our way to our eternal (and heavenly) home (2 Cor. 5:1-8)! Are you living like an alien, or have you settled in and conformed to the ways of this foreign land?