What would you think if someone got a letter in the post, and after opening it just dived into random sections of it, pulling out sentences with no regard to the context in which they were written. Would you think that would be a sensible way to go about establishing the intent of the writer and the meaning of his correspondence? I would guess your answer is no, but then why do so many people adopt that approach when dealing with Scripture?
Let me give just one example of this "proof text" approach to the Bible. In Paul's letter to the Romans he writes, "To them who by patient continuance in well doing seek for glory and honour and immortality, eternal life...glory, honour, and peace, to every man that worketh good...the doers of the law shall be justified" (Romans 2 v 7, 10, 13). "There you go - salvation is by good works" some say. However, Paul is in the midst of an argument here, so please don't fold up the letter and put it away! Keep reading - he's going to reach a conclusion soon. What he is saying in the verses picked out above is this - if someone continually and completely lives as they should, and keeps God's law then they'll have no sins for which to be punished, and they'll have earned acceptance with God, but Paul goes on to say that no one has done that!
In chapter 3 he says there is none righteous in regard to God's law (v10), there's none that continually does good (v12). He says that the whole world is guilty before God (v19), that all have sinned (v23). So his point is that none of us fulfil God's perfect moral demands and requirements - we are all guilty sinners, and none of us can be accepted by God on the basis of the life we have lived, but rather the life we have lived is the reason we need salvation and forgiveness. A person who has broken the law cannot point to that law as the basis for his justification - it is that law that condemns him! Therefore Paul's conclusion to his argument is this: "Therefore we conclude that a man is justified by faith apart from the deeds of the law" (Romans 3 v 28). We need to put our faith in the one who bore the punishment our crimes deserve.
If you fulfil the requirements of Romans 2 v 7, 10 & 13, i.e. if you are 100% perfect, then you can ignore the Gospel - you don't need it. But none of us meet that standard - we all have broken the law, and that's why we all need the salvation offered in the Gospel, you can't afford to ignore it.
