A Christian - what exactly do you mean?
-> They have exercised saving faith in the only Savior, Jesus Christ. (John 3:15-18)
-> God has forgiven them of their sins - past, present and future. (Acts 10:43)
-> God has made them a child of His. (Acts 8:15-17)
-> God has made them into a new creation. (2 Corinthians 5:17)
-> They are indwelled by the Holy Spirit of God. (1 Corinthians 3:16)
While a full heart-, mind-, and soul love for God should be the priority in the life of every Christian, sadly, like our love for the earthly things in our lives, our love for God can, and does fluctuate in its intensity.