As the saying goes, "you can leave the Church, but you can never leave it alone." So it is with an apostate, they can try all they want to ignore the kingdom of God but they will inevitably find themselves fighting against the Church and kicking against the pricks. Peter explained it as follows:
'For if after they have escaped the pollutions of the world through the knowledge of the Lord and Saviour Jesus Christ, they are again entangled therein, and overcome, the latter end is worse with them than the beginning.
For it had been better for them not to have known the way of righteousness, than, after they have known it, to turn from the holy commandment delivered unto them.
But it is happened unto them according to the true proverb, The dog is turned to his own vomit again; and the sow that was washed to her wallowing in the mire.' (2 Pet 2:20-22)
The words of Paul are also instructive:
'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.' (Heb 6:4-6)
Joseph Smith
"Strange as it may appear at first thought, yet it is no less strange than true, that notwithstanding all the professed determination to live godly, apostates after turning from the faith of Christ, unless they have speedily repented, have sooner or later fallen into the snares of the wicked one, and have been left destitute of the Spirit of God, to manifest their wickedness in the eyes of multitudes. From apostates the faithful have received the severest persecutions. Judas was rebuked and immediately betrayed his Lord into the hands of his enemies, because Satan entered into him. There is a superior intelligence bestowed upon such as obey the Gospel with full purpose of heart, which, if sinned against, the apostate is left naked and destitute of the Spirit of God, and he is, in truth, nigh unto cursing, and his end is to be burned. When once that light which was in them is taken from them, they become as much darkened as they were previously enlightened, and then, no marvel, if all their power should be enlisted against the truth, and they, Judas like, seek the destruction of those who were their greatest benefactors." (Teachings of the Prophet Joseph Smith, p. 67.)
Joseph Smith
"After a man has sinned against the Holy Ghost, there is no repentance for him. He has got to say that the sun does not shine while he sees it; he has got to deny Jesus Christ when the heavens have been opened unto him, and to deny the plan of salvation with his eyes open to the truth of it; and from that time he begins to be an enemy. This is the case with many apostates of the Church of Jesus Christ of Latter-day Saints."
"When a man begins to be an enemy to this work, he hunts me, he seeks to kill me, and never ceases to thirst for my blood. He gets the spirit of the devil-the same spirit that they had who crucified the Lord of Life-the same spirit that sins against the Holy Ghost. You cannot save such persons; you cannot bring them to repentance; they make open war, like the devil, and awful is the consequence." (Teachings of the Prophet Joseph Smith, p. 358)
Joseph Fielding Smith
"The testimony of the Spirit is so great, and the impressions and revelations of divine truth so forcefully revealed that there comes to the recipient a conviction of the truth that he cannot forget. Therefore, when a person once enlightened by the Spirit so that he receives knowledge that Jesus Christ is the Only Begotten Son of God in the flesh, then turns away and fights the Lord and his work, he does so against the light and testimony he has received by the power of God. Therefore, he has resigned himself to evil knowingly. Therefore Jesus said there is no forgiveness for such a person." (Answers to Gospel Questions, vol. 4, p. 92)
Neal A. Maxwell
"Then there are the dissenters who leave the Church, either formally or informally, but who cannot leave it alone. Usually anxious to please worldly galleries, they are critical or at least condescending towards the Brethren. They not only seek to steady the ark but also on occasion give it a hard shove! Often having been taught the same true doctrines as the faithful, they have nevertheless moved in the direction of dissent (see Alma 47:36). They have minds hardened by pride (see Daniel 5:20)." (Men and Women of Christ, p. 4)