God saved us from our sin, and to do so he had to give his one and only Son! (John 3:16) How painful it must have been for Jesus here on Earth, but He endured through the paid to bring us closer to Him! Sometimes, we must also endure pain and hardship in this world to bring someone back to salvation and eternal life. Not only can it be physically painful, but it can be spiritually and emotionally painful to walk with someone when they are so clearly walking away from you and God.
God is love, therefore love is what we need to do when we want to save someone from their sin. (1 Peter 4:8) This sounds easy enough, but how do you tell a fellow Christian that what they are doing is wrong in a loving way, well believe it or not the Bible has instructions on that too! Matthew 18:15-20 tells us that there is a way to tell a fellow Christian that what they are doing is wrong, and it is in love. I would always suggest approaching God first, for strength, endurance, wisdom, and courage. Often this process of helping someone back to God can be a long process, so make sure that you rely on God’s strength and not your own. After you have talked to God, take the person aside and point out their sin. This sounds rude, but as Christians we are called to sharpen each other (Proverbs 27:17), this does not mean point out their every fault, but it means that we need to build each other up, if this includes fixing the foundation of their faith, then yes point out the sin.
I have often made the mistake of sending a Facebook message or text message, and this has always back fired on me, I believe that the process mentioned in Matthew 18 needs to be done in person, I believe that this allows God to be present to the both of you, and when is that ever a bad thing.
One thing I have learned over the years, is that God does not work on our schedule. Sometimes, there is a lesson that you or the person you are trying to help needs to learn before this sin can be resolved. God is not here to relieve us of the consequences of our sin, but to save us from the sin itself. Remember, God does not work on your schedule so do not expect.
“Never, in peace or war, commit your virtue or your happiness to the future. Happy work is best done by the man who takes his long-term plans somewhat lightly and works from moment to moment ‘as to the Lord.’ It is only our daily bread that we are encouraged to ask for. The present is the only time in which any duty can be done or any grace received.” —from The Weight of Glory by C.S. Lewis