1 John 3:6 - Exposition

Every one that abideth in Christ ipso facto sinneth not; for, if he sins, he ceases to abide in him. Just in so far as he abides, he does not sin. Or it may mean that be who abides in Christ cannot deliberately and habitually sin. But then would not St. John have written, "He that abideth in Christ abideth not in sin"? But the main difficulty is in the second half. In what sense is it true that every one that sinneth hath not seen Christ? In the main two explanations are given.