Below is an illustration I did use in my last sermon. The passage I was preaching on was Mark 3:31-35 on Who is Jesus'family. I started by explaining that when Jesus defined who was in and who was out of His family He was actually saying who was in and out of His kingdom. Flesh and blood, lineage from Abraham, doesn't do it. You must be reborn "from above" (John 3) and adopted into His family. I used ben hur as a type of Roman adoption. Then we looked at some verses from Romans8 and Ephesians 1 on the benefits of being His adopted child. Then I brought in this illustration:
Watchman Nee tells about a new convert who came in deep distress to see him. "No matter how much I pray, no matter how hard I try, I simply cannot seem to be faithful to my Lord. I think I'm losing my salvation." Nee said, "Do you see this dog here? He is my dog. He is house-trained; he never makes a mess; he is obedient; he is a pure delight to me. Out in the kitchen I have a son, a baby son. He makes a mess, he throws his food around, he fouls his clothes, he is a total mess. But who is going to inherit my kingdom? Not my dog; my son is my heir. You are Jesus Christ's heir because it is for you that He died." We are Christ's heirs, not through our perfection but by means of His grace.
From there i finished by talking about how, if we are members of His family, we should be demonstrating the family likeness, ie love. Love is an action. Love is servanthood. if we are loving we will be involved in the messy work of digging up and weeding while Christ produces the fruit of the Spirit in us. Or we can stay clean and comfortable and just be plastic flowers!