...pre trib post trib, what does it really matter...
I believe knowing the rapture's timing matters because Jesus said it's possible for those who believe to subsequently "be offended" by tribulation and fall away:
"The same is he that heareth the word, and anon with joy receiveth it; Yet hath he not root in himself, but dureth for a while: for when tribulation or persecution ariseth because of the word, by and by he is offended" (Matthew 13:20-21).
"Then shall they deliver you up to be afflicted, and shall kill you: and ye shall be hated of all nations for my name's sake. And then shall many be offended, and shall betray one another, and shall hate one another. And many false prophets shall rise, and shall deceive many. And because iniquity shall abound, the love of many shall wax cold" (Matthew 24:9-12).
"They, which, when they hear, receive the word with joy; and these have no root, which for a while believe, and in time of temptation [peirasmos] fall away" (Luke 8:13).
"Beloved, think it not strange concerning the fiery trial which is to try [peirasmos] you, as though some strange thing happened unto you: But rejoice, inasmuch as ye are partakers of Christ's sufferings; that, when his glory shall be revealed, ye may be glad also with exceeding joy" (1 Peter 4:12-13).
I don't believe someone necessarily will fall away because they believe in a pre-trib rapture, or won't fall away because they believe in a post-trib rapture, but true believers -- whether pre-trib or post-trib -- can fall away in tribulation.
And I believe Jesus told us everything we'd have to face beforehand for a good reason, so that we'd be less likely to be offended and fall away: "Take ye heed: behold, I have foretold you all things" (Mark 13:23). "My people are destroyed for lack of knowledge" (Hosea 4:6). To be forewarned is to be forearmed: mentally, emotionally, and spiritually (and possibly even physically, if the Lord so leads).
I believe the pre-trib doctrine may be setting up many in the church for great disappointment and confusion and the falling away from the faith: "The Spirit speaketh expressly, that in the latter times some shall depart from the faith" (1 Timothy 4:1), and this departure from the faith will happen before Jesus comes to rapture us: "We beseech you, brethren, by the coming of our Lord Jesus Christ, and by our gathering together unto him... Let no man deceive you by any means: for that day shall not come, except there come a falling away first" (2 Thessalonians 2:1, 3).
I believe we all -- whether we are pre-trib or post-trib -- must in these days begin to face and get free of any fear of tribulation and any fear of death, as Christians have always been exhorted to:
"Fear none of those things which thou shalt suffer: behold, the devil shall cast some of you into prison, that ye may be tried; and ye shall have tribulation ten days: be thou faithful unto death, and I will give thee a crown of life" (Revelation 2:10).
"He that overcometh shall inherit all things; and I will be his God, and he shall be my son. But the fearful... shall have their part in the lake which burneth with fire and brimstone" (Revelation 21:7-8).
"Deliver them who through fear of death were all their lifetime subject to bondage" (Hebrews 2:15).
"Be not afraid of them that kill the body, and after that have no more that they can do" (Luke 12:4).
"For to me to live is Christ, and to die is gain. But if I live in the flesh, this is the fruit of my labour: yet what I shall choose I wot not. For I am in a strait betwixt two, having a desire to depart, and to be with Christ; which is far better" (Philippians 1:21-23).
I believe some teachers may unwittingly be giving the people what they want to hear (2 Timothy 4:3-4), instead of what they need to hear (Mark 13:23), just as happened in the days of old (Jeremiah 14:13-15, Ezekiel 13:2-16).
I expect Satan will use the failure of a pre-trib rapture to happen as a great weapon against Christians who believed with all their heart that Jesus had promised them a pre-trib rapture. He could say something like: "Jesus promised you that he would whisk you away before the tribulation started, but did he keep his word? No. Just like he kicked your parents Adam and Eve out of the garden of Eden to keep them from eating from the tree of life and living forever, as it says in Genesis 3:22-23, so even now he doesn't want the best for you; he just wants you and your baby there to suffer and starve to death for his amusement! You don't believe me? Read it for yourself in Job 9:22-23 and Proverbs 1:26. But look here, I'm not laughing at you, I'm offering you and your baby food to eat. Why? Because unlike him I care about what happens to you. All you need to do is take this little mark on your hand or forehead and worship me and my man here for a little bit and we'll take perfect care of you; and once we're all united we'll storm heaven together and I'll let you eat of the tree of life and live forever and do as you please."
I believe it's possible that some Christians, desperate in their suffering and the suffering of their little ones, could fall for this deception, for haven't many already fallen for a false gospel which says Jesus saved them from the tribulation?
"They shall pass through it, hardly bestead and hungry: and it shall come to pass, that when they shall be hungry, they shall fret themselves, and curse their king and their God, and look upward. And they shall look unto the earth; and behold trouble and darkness, dimness of anguish; and they shall be driven to darkness" (Isaiah 8:21-22).
...Why aren't you spending this much energy on talking to the unsaved about Jesus?...
I've heard the gospel preached in this manner: "Get saved now or you'll have to go through the great tribulation. God has promised all believers a rapture before the tribulation." What could happen to the faith of some of those saved on this basis, if there's no rapture before the tribulation? Could some begin to think they were sold a bill of goods, that the gospel is a sham?
I believe the gospel we preach must include everything that Jesus taught (Matthew 28:20), including what we must face before he comes to gather us together (Matthew 24:3-31).