One of your articles discussed that a person who leaves the church and rejects God has no more sacrifice for sin. Can these people be brought back into the fold?
Yes, provided they sincerely desire to come back. The book of Hebrews deals more with this issue of falling away than does any other book in the New Testament because so many Jewish Christians were falling away from the church to go back to Judaism. In Hebrews 6:4-6 we read, "For it is impossible for those who were once enlightened, and have tasted of the heavenly gift, and were made partakers of the Holy Ghost, And have tasted the good word of God, and the powers of the world to come, If they shall fall away, to renew them again unto repentance; seeing they crucify to themselves the Son of God afresh, and put him to an open shame." Please understand what this passage is saying. Here are people who were Christians. They were "once enlightened." They had "tasted of the heavenly gift." They partook of the Holy Spirit. They experienced the "good word of God." They partook of the "powers of the world to come." Yet, they made a conscious choice to refuse these things, forsake Christianity and go back into Judaism. The Hebrew writer says that it is "impossible to renew them again unto repentance." I take this to mean that no outside force is going to be able to bring them back to faithfulness to the Lord.
Now, can they come back? There is no doubt that they can repent and turn back to God again. The story of the Prodigal Son in Luke 15:11-32 illustrates this very point. God is always willing to accept those who, in repentance, turn to Him and declare their love for Him. The Prodigal Son is an illustration of the very point that we need to make in this regard, so let's look at that. Notice that the Prodigal Son left his father of his own will. He was in a good and blessed situation, but he decided that he knew what was best and left his father's house. As a result, he squandered his inheritance living a sinful life. He eventually ran out of money and friends, and ended up in the lowest situation imaginable in that day--feeding pigs. When he himself realized the depravity of his situation, he decided to make a change. He came home and was restored to his father. His father forgave him and received him back into his house. The one thing that you don't read about in the story of the prodigal son is people going out to check on him to make sure he was well. The father didn't go looking for him; the servants didn't go looking for him and the brother didn't go looking for him. They didn't look for him because in his situation there would be nothing that could be said to bring him back.
Now, there are situations where we should look for those who are lost. This is illustrated in the parable of the lost sheep and lost coin that are told immediately before the parable of the Prodigal Son. The lost sheep illustrates those who are lost through ignorance. The lost coin illustrates those who are lost through neglect. However, when one deliberately chooses to leave that which he knows is a place of rest and safety, then the only way that person can be restored is through their own personal decision. No amount of reasoning from us is going to persuade someone to come back who has purposefully chosen to be lost. So as the Hebrew writer said in Hebrews 6:4-6, it is impossible for us to renew them again to repentance. That is a choice that only that person can make. What must one do to come back? He needs to acknowledge his lost state. And since this question is addressing Christians, this means making a public confession of fault and recommitting oneself to the cause which was publicly abandoned.