I believe the meaning of “the doers of the law shall be justified” is that if you attempt to do the deeds of the law in order to be justified then you have to do it perfectly.
Does this sound as if they're 'doing it' perfectly? Note the conflict(s):
13 for not the hearers of the law are just before God, but
the doers of the law shall be justified:
14 (for when Gentiles that have not the law
do by nature the things of the law, these, not having the law, are the law unto themselves;
15 in that they show
the work of the law written in their hearts, their conscience bearing witness therewith, and
their thoughts one with another accusing or else excusing them); Ro 2
22 For
I delight in the law of God after the inward man:
23 but
I see a different law in my members, warring against the law of my mind, and bringing me into captivity under the law of sin which is in my members.
24 Wretched man that I am! who shall deliver me out of the body of this death?
25 I thank God through Jesus Christ our Lord. So then
I of myself with the mind, indeed, serve the law of God; but with the flesh the law of sin. Ro 7
14 For
the whole law is fulfilled in one word, even in this: Thou shalt love thy neighbor as thyself.
15 But if ye bite and devour one another, take heed that ye be not consumed one of another.
16 But I say, walk by the Spirit, and ye shall not fulfil the lust of the flesh.
17 For
the flesh lusteth against the Spirit, and the Spirit against the flesh; for these are contrary the one to the other; that ye may not do the things that ye would. Gal 5
if you attempt to do the deeds of the law in order to be justified then you have to do it perfectly
The saints don't have to 'attempt', the desire to do good comes 'naturally', and the 'fulfillment' of it has been made simple to grasp:
12 All things therefore
whatsoever ye would that men should do unto you, even so do ye also unto them: for
this is the law and the prophets. Mt 7
8 Owe no man anything, save to love one another: for
he that loveth his neighbor hath fulfilled the law. Ro 13
14 For
the whole law is fulfilled in one word, even in this: Thou shalt love thy neighbor as thyself. Gal 5
8 Howbeit if ye
fulfil the royal law, according to the scripture,
Thou shalt love thy neighbor as thyself, ye do well: Ja 2