***DISCLAIMER***The following is far from an exhaustive post. Instead, it makes a best effort to sufficiently answer the question.
Recently, someone asked me about what the Bible would say about the phrase, “All Is Fair In Love and War.” This was an interesting question. Below is my response.
“All is Fair in Love and War” is a complicated phrase. Dictionary.com notes how this “proverb” (it is not a biblical one) is “frequently used when two people are contending for the love of a third.” The Cambridge Dictionary defines the phrase as, “in love and war you do not have to obey the usual rules about reasonable behavior.” This essentially gives free reign for one to do whatever he/she wants to get the one he/she wants. This may compel someone to lie, cheat, steal, gossip, hurt, kill and/or covet, among other things. While it does not guarantee that those undesirable actions will occur, the fact obedience to the “usual rules about reasonable behavior” is not a requirement is not a good thing.
The Bible says nothing about the aforementioned phrase verbatim. However, given the nature of the aforementioned phrase, it is safe to say that the Bible would have to view the phrase as an abomination at the very least. After all, the end goal is for a person to get the one he/she wants by any necessary means. In a nutshell, the phrase completely serves self instead of others.
No less than two passages show the futility of the phrase, “All Is Fair In Love And War.”
Colossians 3:1-17 (NASB):
Therefore if you have been raised up with Christ, keep seeking the things above, where Christ is, seated at the right hand of God. 2 Set your mind on the things above, not on the things that are on earth. 3 For you have died and your life is hidden with Christ in God. 4 When Christ, who is our life, is revealed, then you also will be revealed with Him in glory.
5 Therefore consider the members of your earthly body as dead to immorality, impurity, passion, evil desire, and greed, which amounts to idolatry. 6 For it is because of these things that the wrath of God will come upon the sons of disobedience, 7 and in them you also once walked, when you were living in them.8 But now you also, put them all aside: anger, wrath, malice, slander, and abusive speech from your mouth. 9 Do not lie to one another, since you laid aside the old self with its evil practices, 10 and have put on the new self who is being renewed to a true knowledge according to the image of the One who created him— 11 a renewal in which there is no distinction between Greek and Jew, circumcised and uncircumcised, barbarian, Scythian, slave and freeman, but Christ is all, and in all.
12 So, as those who have been chosen of God, holy and beloved, put on a heart of compassion, kindness, humility, gentleness and patience; 13 bearing with one another, and forgiving each other, whoever has a complaint against anyone; just as the Lord forgave you, so also should you. 14 Beyond all these things put on love, which is the perfect bond of unity. 15 Let the peace of Christ rule in your hearts, to which indeed you were called in one body; and be thankful. 16 Let the word of Christ richly dwell within you, with all wisdom teaching and admonishing one another with psalms and hymns and spiritual songs, singing with thankfulness in your hearts to God. 17 Whatever you do in word or deed, do all in the name of the Lord Jesus, giving thanks through Him to God the Father.
Here, the Apostle Paul instructs his audience to keep seeking things above (v. 1). He also tells the audience to set its mind on things above and the reason why to do so (vv. 2-3). There is also a call to consider dead to the body “immorality, impurity, passion, evil desire, and greed, which amounts to idolatry” in addition to a call to put aside lying, “anger, wrath, malice, slander and abusive speech from your mouth” (vv. 5, 8-9). Finally, Paul concludes the noted passage with an admonition to do all in word and deed in the name of the Lord Jesus (v. 17). Given the fact that “All Is Fair In Love And War” does not require the rules of reasonable behavior to be followed, this unashamedly opens the door for immorality, impurity, passion, evil desire, greed, idolatry, anger, malice, wrath, slander and abusive speech to occur. Moreover, some of these things are an abomination to the LORD (see Proverbs 6:16-19). Finally, the phrase does not have “pleasing God” as a priority. Instead, it focuses on pleasing self. After all, if the end game is for one to get whomever he/she wants by whatever means, how is it pleasing God or neighbor, especially if it is not being done in the name of the Lord Jesus?
Galatians 5:13-26 (NASB):
13 For you were called to freedom, brethren; only do not turn your freedom into an opportunity for the flesh, but through love serve one another. 14 For the whole Law is fulfilled in one word, in the statement, “You shall love your neighbor as yourself.”15 But if you bite and devour one another, take care that you are not consumed by one another.
16 But I say, walk by the Spirit, and you will not carry out the desire of the flesh.17 For the flesh sets its desire against the Spirit, and the Spirit against the flesh; for these are in opposition to one another, so that you may not do the things that you please. 18 But if you are led by the Spirit, you are not under the Law. 19 Now the deeds of the flesh are evident, which are: immorality, impurity, sensuality,20 idolatry, sorcery, enmities, strife, jealousy, outbursts of anger, disputes, dissensions, factions, 21 envying, drunkenness, carousing, and things like these, of which I forewarn you, just as I have forewarned you, that those who practice such things will not inherit the kingdom of God. 22 But the fruit of the Spirit is love, joy, peace, patience, kindness, goodness, faithfulness, 23 gentleness, self-control; against such things there is no law. 24 Now those who belong to Christ Jesus have crucified the flesh with its passions and desires.
25 If we live by the Spirit, let us also walk by the Spirit. 26 Let us not become boastful, challenging one another, envying one another.
Here, the Apostle Paul tells his audience to serve one another through love (v. 13). He also states that the phrase “You shall love your neighbor as yourself” fulfills the whole Law (v. 14). In verse 15, he tells his audience members to take care not to be consumed by one another if they bite and devour one another. Given the fact the phrase “All Is Fair In Love And War” primarily features two people contending for a third while giving little to no consideration to the “usual rules about reasonable behavior”, would it be surprising if these two people bit and devoured each other in their respective routes of pursuing the mutual third party? Furthermore, is choosing not to play by the “usual rules about reasonable behavior” tantamount to serving one another in love?
In verses 19-21, Paul lists both the deeds of the flesh and the consequences of practicing them. He then lists the fruits of the Spirit in verses 22-23. If the phrase “All Is Fair In Love And War” cared about the “usual rules about reasonable behavior”, then love, joy, peace, patience, kindness, gentleness, goodness, faithfulness and self-control would be important things to consider. However, because the phrase does not do such a thing, those who hold to such a belief are more likely to manifest the deeds of the flesh.
Finally, Proverbs 8:13 states, “The fear of the LORD is to hate evil; Pride and arrogance and the evil way And the perverted mouth, I hate.” It is evil to practice any of the deeds of the flesh (Galatians 5:19-21) as well as any of the things Paul urged the church at Colossae to put away (Colossians 3:5-9). Adhering to the phrase “All Is Fair In Love And War” allows the possibility for such evil things to be practiced. As the passage in Proverbs notes, the LORD hates evil. Given the aforementioned phrase’s lack of emphasis on following the “usual rules about reasonable behavior”, God’s Word would have to say that the aforementioned phrase is an abomination that focuses on pleasing self rather than glorifying God.