While we view the heart as the seat of our emotions and our will, Israel understood the heart to be the center of the whole person—not just the source of emotions and will but also of wisdom and perspective.In essence, the heart referred to who you are as a person.
Paul says: Paul advises a believer who is married to an unbeliever that they cannot presume they will "save" their spouse.
So if a believer marries an unbeliever with the expectation of converting their spouse, they commit a sin, because they openly disobey the word of God without cause to expect success.
Moreover, they are signing up potentially for a life of spiritual difficulty, which carries eternal consequences.
Since the unbeliever cannot please God without faith (and the believing spouse has no expectation of changing their situation), then by necessity the unbeliever will become the stronger "ox" in the relationship.
If you are too afraid to talk to either of them about an aspect of your relationship, then you probably shouldn’t be involved in it. To understand why you should guard your heart, you must understand what Israel would have understood Solomon to be saying in Proverbs .
Most importantly, they did not understand this passage to have anything to do with Americanized dating.So, guarding your heart is the result of clear communication.It begins with prayer to God (as Paul lays out in Philippians 4:6-7) and overflows into communication with the other person. The Bible's teaching on this question is simple, clear and unequivocal: a believer may only marry another born-again believer.To do otherwise is a sin that carries potentially life-long, negative spiritual consequences and personal hardship.There is only one other verse in the Bible that uses the phrase “guard your heart.” That verse gives us the answer to the question of how to guard your heart in life and, particularly, in dating.