I would second the recommendation that you read John Bunyan's Grace Abounding to the Chief of Sinners. John Bunyan, who by the way, was the author of Pilgrim's Progress, found himself in your exact position, wrestling with the same verses.
What follows are some extracts from His book Grace Abounding to the Chief of Sinners. I encourage you to read the whole book, you can read it online at..;
http://www.ccel.org/ccel/bunyan/grace.html
Now began my heart again to ache and fear I might meet with disappointment at the last, wherefore I began, with all seriousness, to examine my former comfort, and to consider whether one that had sinned as I have done, might with confidence trust upon the faithfulness of God, laid down in those words by which I had been comforted and on which I had leaned myself. But now were brought those sayings to my mind, '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' (Heb. 6.4-6). 'For if we sin wilfully after that we have received the knowledge of the truth, there remaineth no more sacrifice for sins, but a certain fearful looking for of judgment and fiery indignation, which shall devour the adversaries' (Heb. 10.26, 27). Even 'as Esau, who for one morsel of meat sold his birthright; for ye know how that afterward, when he would have inherited the blessing, he was rejected; for he found no place of repentance, though he sought it carefully with tears' (Heb. 12.16, 17) .
Now was the word of the gospel forced from my soul, so that no promise or encouragement was to be found in the Bible for me; and now would that saying work upon my spirit to afflict me, 'Rejoice not, O Israel, for joy as other people' (Hos. 9.1). For I saw indeed there was cause of rejoicing for those that held to Jesus; but as for me, I had cut myself off by my transgressions, and left myself neither foot-hold, nor hand-hold, amongst all the stays and props in the precious word of life...
Then that scripture gave me hope, 'I will never leave thee nor forsake thee' (Heb. 13.5). O Lord, said I, but I have left Thee. Then it answered again, 'But I will not leave thee.' For this I thank God also...
Now as touching this, that Esau sought a place of repentance; thus I thought, first, This was not for the birthright, but for the blessing; this is clear from the apostle, and is distinguished by Esau himself; 'He took away my birthright (that is, formerly); and behold, now he hath taken away my blessing' (Gen. 27.36). Secondly, Now, this being thus considered, I came again to the apostle, to see what might be the mind of God, in a New Testament style and sense, concerning Esau's sin; and so far as I could conceive, this was the mind of God, that the birthright signified regeneration, and the blessing the eternal inheritance; for so the apostle seems to hint, 'Lest there be any profane person, as Esau, who for one morsel of meat sold his birthright'; as if he should say, Lest there be any person amongst you that shall cast off all those blessed beginnings of God that at present are upon him, in order to a new birth, lest they become as Esau, even be rejected afterwards, when they would inherit the blessing.
For many there are who, in the day of grace and mercy, despise those things which are indeed the birthright to heaven, who yet, when the deciding day appears, will cry as loud as Esau, 'Lord, Lord, open to us'; but then, as Isaac would not repent, no more will God the Father, but will say, I have blessed these, yea, and they shall be blessed; but as for you, depart from me, all ye workers of iniquity (Gen. 27.33; Luke 13.25-27).
When I had thus considered these scriptures, and found that thus to understand them was not against, but according to other scriptures; this still added further to my encouragement and comfort, and also gave a great blow to that objection, to wit, that the scripture could not agree in the salvation of my soul. And now remained only the hinder part of the tempest, for the thunder was gone beyond me, only some drops did still remain, that now and then would fall upon me; but because my former frights and anguish were very sore and deep, therefore it did oft befal me still, as it befalleth those that have been scared with fire, I thought every voice was Fire, fire; every little touch would hurt my tender conscience.
But one day, as I was passing in the field, and that too with some dashes on my conscience, fearing lest yet all was not right, suddenly this sentence fell upon my soul, Thy righteousness is in heaven; and methought withal, I saw, with the eyes of my soul, Jesus Christ at God's right hand; there, I say, is my righteousness; so that wherever I was, or whatever I was a-doing, God could not say of me, He wants my righteousness, for that was just before Him. I also saw, moreover, that it was not my good frame of heart that made my righteousness better, nor yet my bad frame that made my righteousness worse; for my righteousness was Jesus Christ Himself, the same yesterday, and to-day, and for ever (Heb. 13.8).
Now did my chains fall off my legs indeed, I was loosed from my affliction and irons, my temptations had fled away; so that, from that time, those dreadful scriptures of God left off to trouble me now; now went I also home rejoicing, for the grace and love of God.