You have heard the words of Apostle Paul in 2 Corinthians 6:14 - "Be not unequally yoked with unbelievers". However, permit me to say that there is also an unequal yoking with 'unbelieving believers'. Unbelieving believers are Christians who have refused to grow spiritually. They have an outlook of godliness but they do not understand nor practice the principles of spiritual growth. They are not inclined towards sowing spiritual seeds therefore they not experience the concomitant rewards of such exercise. They do not perceive the need for fervent pursuit of God nor do they know how to go about it. They are active in church activities but spiritually stagnant and retrogressing.
When you begin to operate below what your potential and your will can accomplish due to your association/relationship with such people, you can be said to be unequally yoked. In the ancient agricultural setting, ploughing was carried out using animals- oxen that were of the same size, height, weight, and strength, usually born around the same period. If the farmer goes contrary to this principle, the ploughing is hampered. He will not get good results because the stronger ox will find it hard to work effectively as it is being deterred by the weak one while the week ox will feel strained by the stronger ox. Progress of the ploughing will be affected adversely in the end.
Many young and zealous Christians get hampered along the way in their Christian walk due to association with certain kinds of people. Having decided to serve God with their talent (potential), time and resources, denying themselves of the pleasure of youthful delight and committing to the course of the Gospel wholly and totally, then something goes wrong. For instance, you take advantage of every opportunity that comes your way to be of service to God and to humanity especially in your local assembly but on the other hand is your colleague at work who is also a friend in church (serving in the same department); he looks for every 'legitimate' reason to stay away from church meetings. This attitude begins to irritate you and then you are getting afraid that your relationship might become strained. You spend a lot of time searching out God's perspective in order that you will align your world-view with His (God's) but your friend thinks you are getting on the extreme. Yes! Your relationship might soon fall- apart and until you detach, you will not function maximally.
When it does not look like your friend is striving to attain you level of spiritual fervency or even go beyond that level, the Bible says to strain such relationship (1 Corinthians 5:1-13). Paul warns us against Christians who live like unbelievers. He did not say to tolerate and manage such people because the truth is that their evil will undoubtedly influence good people. Instead, he advised that people with such attitude should be quarantined so others don't take after their attitude of lukewarmness.
Paul warned the Galatians who had begun to entertain the company of people with erroneous beliefs (Judaism). He vehemently kicked against such people and their false doctrines. He wished that they were removed from among the Galatians because only then would his teachings begin to have lasting impact on the Galatians.
Titus was with me, and although he is Greek, no one forced him to be circumcised. False Christians were brought in. They slipped in as spies to learn about the freedom Christ Jesus gives us. They hoped to find a way to control us. But we did not give in to them for a moment, so that the truth of the Good News would always be yours. Galatians 2:3-5 GW
You were doing so well. Who stopped you from being influenced by the truth? The arguments of the person who is influencing you do not come from the one who is calling you. A little yeast spreads through the whole batch of dough. The Lord gives me confidence that you will not disagree with this. However, the one who is confusing you will suffer God's judgment regardless of who he is. Galatians 5:7-10 GW
Note that Paul did not decide to tolerate the perpetrators of Judaism by trying to convince them, he simply disallowed them.
The situations that we face today may not be as serious as the ones discussed above but the same principles do apply. If you find yourself in company with people who have ideas, opinions and viewpoints different from that which you have searched the scriptures and found out to be true (to be the will of God) you must be watchful and get ready to apply the above principle. When you find yourself in close ties with people whose level of quest and desire to love and please God is little compared to yours, there might be danger somewhere along the line.
You use steel to sharpen steel, and one friend sharpens another. Proverbs 27:17 MSG
One deep sea calls to another... Psalms 42:7 GW
I am not down playing on the importance of one believer helping another believer and to be strong and to grow spiritually. That is very important but at this point, we are looking at where area of influence is concerned. 1 Corinthians 15:33 says: Do not be so deceived and misled! Evil companionships (communion, associations) corrupt and deprave good manners and morals and character (AMP). It amazes me that it is 'evil' that corrupts the 'good' and not the 'good' changing the 'evil'. The category of people I discussed in the first paragraph are not 'evil' people per say but they are lukewarm, and mediocre therefore you are not sure where their appetite actually is.
You are indeed a light in the world to shine that men might see (Matthew 5:16), therefore you must stay away from pollutants else your light will not be seen. However, there are some relationships that you cannot strain i.e. kinship/familial ties. In such cases, you must remain unblended and hold on tightly to what you believe. Sometimes, what wins the other person over is not being a little bit relaxed about your convictions (or to compromise) but your tenacity in what you do and believe in.
Check your list of close friends again, are you unequally yoked with unbelieving believers? If you are, take caution in how you deal with them. There can never be a zone of stagnation in life. It is either you are becoming like them or they are becoming like you.
Most importantly, strive to have the right people around you; people who are able to stretch you spiritually beyond the point where you are right now for the path of the righteous is like the shining light that shines brighter and brighter (Proverbs 4:18).