I am not sending this to you to preach religion. I am asking you if you were standing before a Holy God do you think that He would have an issue with your sin if you were standing in front of a Holy God?
Because that is exactly what the Bible tells us. That a Holy God can not be in the presence of sin. So every human being that has ever lived has had the exact same problem. This sin problem. But do you also know that Jesus Christ offers all of us a free gift, the forgiveness of sin. And faith and belief is all God wants from you. So, do you believe that Jesus was the Son of God who came to earth and lived a perfect life? Do you know that God will accept Christ's perfect life and let Christ be your Advocate, so on Judgement Day God doesn't look at all the bad stuff you've done. Instead, God will look at His perfect Son when He see's you. Because Jesus and His perfection literally stand in our place.
Something like that. I would try to lay it out in the most simple terms so they know what the problem is and what the solution is and how it works.
Then in the last sentence just write a quick sentence like "there really is little difference between you and I, I am a sinner too. But I have accepted Christ's free gift of salvation and I know that I will be with God in eternity. I sincerely hope that this has helped you and I do apologize for being so forward, but I have to share this with you because I'm sure neither of us gets free gifts often. At this point, I would recommend for you a good Bible-based church that can answer any questions you have and will surround you with like-minded believers. Just Google bible church in your local area. God bless you!"
Rom 3:23 :
For all have sinned, and come short of the glory of God;
Now that you know that no one is good in God's eyes, how do we then become good? How do we become vindicated before God? The Bible teaches that we need to have Jesus' righteousness but the only way to do that is to come to Him by faith:
That if thou shalt confess with thy mouth the Lord Jesus, and shalt believe in thine heart that God hath raised him from the dead, thou shalt be saved.
For with the heart man believeth unto righteousness; and with the mouth confession is made unto salvation.
Jesus commands everyone everywhere to repent of their sins, to ask for His forgiveness, and to turn from their sins and to put their faith and trust in Him. Repenting means that you are sincerely sorry for all the bad things you have done in life and you want Jesus to change you into his holiness and righteousness.