The answer to the question of what it means to be unequally yoked is clearly addressed in the scripture.
“Do not be unequally yoked with unbelievers. For what partnership has righteousness with lawlessness? Or what fellowship has light with darkness?”, 2 Corinthians 6:14 (ESV).
The intimation is that you will be unevenly matched if you are married with a person who does not believe in God. So, as a Christian the scripture is clearly letting us know that we should not be married or emotional and romantically involved with a non-christian. The more intimate a relationship gets the more important a commonality in faith and believe is. If you already disagree on the basic foundation issues, your lifestyle choices as a believer and your relationship with the individual will be affected.
A lot of people believe that you can make it work, having different believes and still get married. But the issue is that the relationship with your god will suffer if you priorities your spouse. For instance, as a Christian I believe in tithing and giving offerings or love gifts to church. I believe in spending time in devotion, praying and worshipping God. I believe in being filled with the Holy Ghost and speaking in tongues. This will sound very crazy to someone who is not a believer. He/she might say it’s cute and might be okay with it. He/she might be the nicest guy in the world, but eventually the natural trials of life will test the strength of the relationship. The different approaches to solving the problems we are both facing will inevitably cause tension and friction in our relationship. A weak belief system will not be able to handle this wear and tear leading to a relationship break down.
With a little bit of thought and honesty you can see why God commands not to be unequally yoked. However, the question that I have heard a few times now is whether you can be unequally yoked, spiritually miss matched, with someone who is a Christian. I think that it is possible. Coming back to my earlier example of being in a relationship with someone of a different belief, there are lifestyle choices that are attached and connected to your spiritual commitment to God, that will influence the life choices you make. Now imagine you are both Christians, but one of us has a different understanding. Theological differences existed in the bible, too. Just read the book of Acts and you’ll see members of the early church and even some of the apostles disagreeing over scriptures. It’s important to make sure you believe in the same things and understand the bible in the same way.
So, yes, unequal yoked to an unbeliever can include being in the same religion but still having differences in beliefs. A Christian can still have his or her idols, such as alcohol, sex, past relationships and other hidden sins or past habits that are difficult to shake. Yes, we all sin and fall short of the glory of God, but when we make a habit of sinning we are forsaking relationship with him. Our relationship with God is the foundation for our relationship with our spouse, because it is intended to be a reflection of what we have with God.
We Grow in Faith 