I am drawing on some portions of notes that I had to present in a class. As such, there are sentence fragments and other oddities in it that I've yet to edit out. There's a lot more information than is required in order to answer your questions, but setting the context is always a default that I have.
Ultimately, I don't really believe that there is any real justification in reading in the word merely since there's not much about this passage that would allow for it.
(1)Thusly wives be submitting yourselves to your own husbands, so that if any do not believe the word, through the conduct of the wives without a word they will be won (2) when seeing the good conduct in fear of you. (3) Of you the outwardly adornment must not be of plaiting of hair and of wearing of gold or putting on of ornamental clothing, (4) but the secret things of the heart of people with the incorruptible things of meek and peaceable spirit, this is worth much before the eyes of God. (5) For thusly in past times also the holy women, the ones trusting in God adorned themselves, by submitting to their own husbands, (6) as Sarah obeyed Abraham by/when/and calling him Lord. And you become children by doing good and by not fearing anything terrifying. (7) Thusly you husbands be dwelling, according to knowledge, as the weaker vessel giving honor to the woman as also coheirs of grace of life, so that the prayers of you are not hindered.
A. Instructions to Wives (3:1-6)
Submission as Mission (1-2)
Practical Instruction for Conduct (3-4)
Examples and Encouragement (5-6)
B. Instructions to Husbands (7)
Call to Charitable Living (7a)
Reason for the Instruction – Equality Under the Gospel (7b)
1-2: "Likewise" refers back to the slaves - likeness of submission and therefore the motivation for the wife's submission is her reverence for God. Christian wives would be inherently antagonistic to culture because wives, slaves, and children were all expected to worship the gods of the husband. Also, the husband would feel embarrassed and be criticized for his inability to manage his household properly. It is significant that Peter does not address any of these particular aspects of the issue - it is up to the husband and wife to actually navigate the practicalities - this in and of itself could be seen as an attempt to transform society since he's essentially giving families autonomy. By submitting, wives shield Christianity from further accusations of anti-social behavior, but the husband would have to know that the submission of the wife/slave was motivated more by the authority of Christ than by social norms established by moral philosophy. << this would have put the husband in quite the predicament … on the one hand the slave/wife was conforming to societal norms, but on the other he would know that the reason was actually anti-social. >> This would also be the primary way that wives could "win" unbelieving husbands to Christ - through demonstrating compatible morality between society and Christianity without offending social sensibilities by blatantly "teaching" her husband. (Jobes)
This is "in-house" advice. Peter is not calling for all women to submit to all men. Women of the region had some opportunities to engage in private business, serve in public offices, etc. The concept of submission (and "respect" and "defer") would not have been as restrictive than in other regions. Supports the idea that this is to Christians whose spouse does not practice the religion of their mate. Peter's advice cuts against the social grain regarding religion by encouraging them to continue in their religion (Christianity) in a blameless manner instead of taking on their husband's religion. (Witherington)
3-4: Peter's instruction regarding beauty betrays a possibility that enough of these Christian sojourners were wealthy enough to necessitate such a command. Not distinctly Christian since moral philosophers held inner "virtues" above outer appearance. Outer decorations were "perceived as instruments of seduction" and attempts to deceive, which were unnecessary if a wife "stayed at home" << no discussion of cultic practices in which priestesses decorated themselves in this way, though this would certainly disregard the context. Perhaps Jobes does well to ignore this area since it isn't germane to the interpretation. >> (Jobes) Contrast between outward and inward person. This was a common theme in pagan writers. Christian women in Asia Minor had more freedom and greater access to money and to seek such adornment could be viewed as immoral (since it is similar to how prostitutes dressed). v. 4 Stresses the contrast between external and internal beauty. Spirit is probably not the Holy Spirit but the "whole person": (1) context is human behavior, (2) Sarah did not receive the Holy Spirit, (3) In NT Holy Spirit is not a quiet entity. (Witherington)
Understanding this domestic code is essential for understanding the message of 1 Peter. "Willingness to suffer unjustly out of reverence for God in order to follow in the footsteps of Jesus … is a radical break with social expectations of that day just as it is in our own day." Literarily, this passage is situated in a section concerned with living such good lives that pagans would have the opportunity to glorify God, one day. Given Paul's understanding of marriage (Eph. 5) anytime the "submission" of the wife has become the central issue, "Christian marriage has already been distorted." But Peter's audience is not two Christians in a marriage, it is to those who have an unbelieving spouse. Same foundation as Paul, but Peter has apologetic intent where Paul had theological intent. (Jobes) Close correlation between 1 Peter 3:3-5 and 1 Tim 2:9-15 in terms of both vocabulary and substance. Perhaps there is some literary dependence but it's more likely that that both Peter and Paul are drawing upon a standard Christian teaching. (Witherington)