i agree it doesnt make mistakes
It may contradict itself, but that is because of dispensational change
As an example Jesus told the disciples not to take scrip then did
[Mark 6:8 KJV] "And commanded them that they should take nothing for [their] journey, save a staff only; no scrip, no bread, no money in [their] purse:"
[Luke 22:36 KJV] "Then said he unto them, But now, he that hath a purse, let him take [it], and likewise [his] scrip: and he that hath no sword, let him sell his garment, and buy one."
I agree that salvation is progressive
That is why Peter didnt preach the cross
That wasnt revealed til Paul
The verses you mentioned are not contradictions, they just show the leading of the Spirit, that in a certain instance take a scrip in another do not, that is not a contradiction, that is the leading of the Spirit, which he tells us to do different things at different times.
Now concerning Peter:
1Pe 1:18-19
(18) Forasmuch as ye know that ye were
not redeemed with corruptible things, as silver and gold, from your vain conversation received by tradition from your fathers;
(19)
But with the precious blood of Christ, as of a lamb without blemish and without spot:
2Pe 1:1-12
(1) Simon Peter, a servant and an apostle of Jesus Christ, to them that have
obtained like precious faith with us through the righteousness of God and our Saviour Jesus Christ:
(2) Grace and peace be multiplied unto you through the knowledge of God, and of Jesus our Lord,
(3) According as his divine power hath given unto us all things that pertain unto life and godliness, through the knowledge of him that hath called us to glory and virtue:
(4)
Whereby are given unto us exceeding great and precious promises: that
by these ye might be partakers of the divine nature,
having escaped the corruption that is in the world through lust.
(5) And beside this, giving all diligence, add to your faith virtue; and to virtue knowledge;
(6) And to knowledge temperance; and to temperance patience; and to patience godliness;
(7) And to godliness brotherly kindness; and to brotherly kindness charity.
(8) For if these things be in you, and abound, they make you that ye shall
neither be barren nor unfruitful in the knowledge of our Lord Jesus Christ.
(9) But he that lacketh these things is blind, and cannot see afar off, and
hath forgotten that he was purged from his old sins.
(10) Wherefore the rather, brethren, give diligence to make your calling and election sure: for if ye do these things, ye shall never fall:
(11) For so an entrance shall be ministered unto you abundantly into the everlasting kingdom of our Lord and Saviour Jesus Christ.
(12) Wherefore I will not be negligent to put you always in remembrance of these things, though ye know them, and be established in the present truth.
Does not the cross purge us from our old sins, is not the shedding of his blood part of the cross, do we not get his promises through the cross, how is what Peter saying here, not compatible with the cross ? Peter preached the same gospel as Paul, yes Paul may of had a greater revelation of it, yet they still preached the same message.