Exodus 22:21 – “You shall not wrong a sojourner or oppress him, for you were sojourners in the land of Egypt.”
God gives instruction to Israel as they camp out at Sinai receiving the Law from Moses. Twice in this text God tells them not to mistreat the “sojourner”. The traveller, the one just passing through, the immigrant, the alien, the refugee … . The reason they must treat such people with dignity, respect, kindness, is because they too had been sojourners. They were homeless and unwelcome except the the work they could provide for their masters. They have been captives in Egypt for over 400 years and God wants them to remember that they were there just as visitors.

The people of God need to be reminded that they were once sojourners, just like others. We can be very forgetful creatures. We must be. We can look down on sinners, having forgotten that we are saved by grace alone and by works not at all. We forget that there is no difference between us and the abortionist, the rapist, the gay activist, … except God’s grace. We forget that Jesus received the unpopular, the outcasts, women, children, adulterers, tax collectors, thieves, liars, doubters. The New Testament doesn’t list all those sins of course. It merely says that Jesus’ opponents were upset with him for associating with sinners. 
Believers sometimes forget that we are the sinners that Jesus received. The Ephesian church was told by Jesus to remember the height from which they had fallen (Revelation 2:5). They had forgotten their first love. They were experts at seeking out sin and false doctrine in others and Jesus commended them for that. Yet Jesus was still going to shut them down for forgetting their first love. 
Peter tells his recipients that whoever lacks the qualities of faith, virtue, knowledge, self-control, steadfastness, godliness, brotherly affection, and love, has forgotten that he has been cleansed from his past sins (II Peter 1:9). 
The Ephesian church was an enviable bunch. They could test for apostleship, and were intolerant of evil people. They persevered and had their doctrine in place. But they had forgotten – forgotten their first love, forgotten grace, forgotten the wonders of their salvation. They forgot that Christianity is more than Systematics. They forgot not to be satisfied with themselves. They forgot, or didn’t know, that they too were spewing out false doctrine. They forgot that they had been forgiven of past sins. When this happens it gets easy to see others as less than ourselves.  
Like people who want immigration shut down whose ancestors were from everywhere except here, we look at these outsiders as less than worthy of being a part of us. We think the sins we were saved from were small compared to theirs. We think the grace that got to us won’t reach them. We think the purity of the church somehow means not soiling ourselves with sinners. 
Twice in Exodus 22 and 23 God tells the Israelites not to oppress sojourners on the basis that they were sojourners themselves. (22:21, 23:9). It’s almost like this was going to be a major problem for them. Our natural response to outsiders is to shun. We don’t like interlopers into our comfort zones. It is a lot of work to allow those who are different into our little circles. And what God tells us is that we were once outside the circle too. Someone let us into it. We do not have the right to change the rules once we are allowed in. The circles is not big enough yet. There is room for so many more. What great sin is surrounding us and Jesus can save people from all sin. There is  nothing more powerful than the finished work of the cross. If only we could remember.
Sinners are welcome. Not into a false sense of salvation. Not into believing that they are OK just the way they are. But welcome into our lives, into our social gatherings, into our hearts. Because that is how we were received by others when we were sojourners. It is how Jesus found us. It was what He knew He would find and it is what He came for.  Now He says to us – go welcome sinners – for you were sinners in the land as well.