Why do you say "if it was intended for someone else, we don't need to read it?" Are you saying that a poem is only worthwhile to the person it is written to? Are you saying that a story is not worthwhile to anyone else but the intended audience? Naturally, we, as Christians, can take something from the written Scriptures, but not because they are written - they are part of the teachings of the Apostles. Being Christians, Apostolic teachings have meaning to us. It doesn't mean that every verse applies to us literally.
Yes, Paul was speaking to the Thessalonicans, but the successors of the Apostles determined that those two letters were worthwhile reading for subsequent Christians. It doesn't mean that Paul was saying that ANYONE who reads that letter is "of the elect".
And naturally, one should consider what the REST of the Apostolic teachings found in the Scriptures SAY, such as:
And ye shall be hated by everyone for my name, but he that shall persevere unto the end, the same shall be saved Mark 13:13
But after thy hardness and impenitent heart treasures up unto thyself wrath against the day of wrath and revelation of the righteous judgment of God, who will render to everyone according to his deeds: to those who persevered in well doing, glory and honour and incorruption, to those who seek eternal life; but unto those that are contentious and do not obey the truth, but are persuaded by unrighteousness, indignation and wrath. Romans 2:5-8
Beloved, when I gave all diligence to write unto you of the common salvation, it was needful for me to write unto you and exhort [you] that ye should earnestly persevere in the faith which was given once unto the saints. Jude 3
If you believe that the Bible was written for Christians for all ages, then you should heed ALL of it, like the parts about persevering in the faith.
Regards
If you continue to presume what I read and believe, then you will continue to make assertions that are incorrect and ignorant. You have no idea who you are talking to, nor how much I know. It was YOUR assertion that Paul wrote the epistle for the Thessaloniacans, not mine. It was YOU who said he didn’t write it to me. Therefore, it is YOU who made irresponsible and unfounded assertions, not me.
Irishtenor's question was rhetorical. You've proven his point -- the Bible is written to everyone who reads and believes it, by the grace of God, and not just to the Apostles.