To compartmentalize is to place certain things in one place and other things elsewhere. You are keeping things separated from one another. To relieve anxiety when one faces a struggle in their values or faith they seek to separate those from the issues they face so as to allow themselves the freedom to work counter to their faith or values.
With respect to the Christian faith, to say if one is compartmentalizing Christ, you would first have to determine if they actually believe in the God of the Bible. Some people have rewritten the Bible, at least in their minds and hearts so that they tell God what He means rather than letting Scripture speak to them and guide their belief. For them, the Bible may condemn or allow something where their beliefs run contrary. In such a case they no longer believe in the God of Scripture, but a god created in their own image. (See the back of the Jethro Tull, Aqualung album for a good illustration of this.)
Other Christians genuinely struggle with the differences in what they want to be reality, verses what God has said. In this instance one seeks to explain away sin or accept it on some level, believing God will look the other way, or saying “but God is loving” or God is forgiving” or “God… this or that.” This falls under the idea of James 2:17, with the perspective that one says they believe, but their actions are contrary to that belief. James notes that this is no belief at all. Jesus said (Jn. 8:31) “If you really believe, then hold to my teachings.”
You can’t compartmentalize your faith and be living it. While this does not preclude forgiveness when this is being done, it does call to question the sincerity of the faith if nothing changes. Behind the broken and contrite heart (Psalm 51:17) is the spirit that wants to change, and leave their sin behind. (Rom. 6:1-2, “What shall we say then? Are we to continue in sin that grace may abound? By no means! How can we who died to sin still live in it?”)
The Bible is a book of Law and Gospel. The Law holds us accountable for our sins and show us the need for a Savior. “For if we go on sinning deliberately after receiving the knowledge of the truth, there no longer remains a sacrifice for sins” (Heb. 10:26). The Gospel shows us the Savior, when we confess our sin before God.
There are more Facebook Christians (folks who hardly darken the steps of the church or who spend more time on FB than in The Book) than Sunday morning Christians. Sadly, there are more Sunday morning Christians than living and serving week day Christians. The faith is so easy for people to spout off or post, but next to non-existent when it comes to exercising that faith in worship of God. There are many locked in various sexual sins; people who neglect the Word and the preaching of the Word, selfishness abounds, failure to support the work of the church, jealousy, gossip,
We have to walk while we have the light (see Jn 12:35 and 1 John 1:6). These all begin as a 1st Commandment issue, placing something or someone above your relationship with God in compartmentalizing Christ. Faith has to be important enough to go with people when they leave the church on Sunday morning, if they come at all. Christ has to rule our lives. Instead of taking Christ out of certain areas of our life, we should be placing Him into every area of our life. Don’t compartmentalize you faith, unless you are purposely placing Christ in every compartment.