He is Jealous.

[God] is a jealous God. Throughout the Bible He uses the marriage relationship to set for the union of Himself and His people Israel in the Old Testament and that of Christ and the church in the new. In either case He calls unfaithfulness adultery. In Jeremiah He says, 

“Turn O backslidden children…for I am married to you.” 

The book of Hosea is built on this theme. In the New Testament we read that the believer is married to Christ (Rom. 7:4). Paul wrote to the Corinthians, 

“For I am jealous over you with a godly jealousy: for I have espoused you to one husband, that I may present you as a chaste virgin to Christ” (1 Cor. 11:2). 

And James puts it bluntly, 

“You adulterers and adulteresses, know you not that the friendship of the world is enmity with God? Whosoever therefore is a friend of the world is the enemy of God” (Jas. 4:4).

Vance Havner -- Repent or Else, Revell, p. 54.