Proverbs 27:17 (NKJV)
Things like knives, scissors, and various kinds of blades need to be sharpened on a regular basis. If you only use your knife, scissors, or blades without the regular maintenance of sharpening them, then the time will come where you will no longer be able to use them effectively. If you keep cutting instruments sharp, it is not a problem to cut through whatever it is you need to cut. It is easy for some of these things to be dulled through normal use, and without those things being sharpened they will end up dull and useless.
The things that we do and the people we spend our time with will have an impact on us. It is interesting to see that people can do many of the right things, but if they spend a lot of time with the wrong kind of people it will have more of a negative impact on them than the positive things that they do will have. The people we spend our time with should be those who help us stay spiritually sharp and do more for God, people that discourage us and take our focus away from the things of God are really just making us dull.
The Bible talks about the kind of people we need to be and the kind of people we need to spend our time with. Yes, we can walk in love and be kind to everyone. But, the question is whether or not we have people in our life who are helping to build us up, people who help us to be "sharp". Do the people we spend our time with help us to be "sharp" and godlier, or do they dull us to the things of God? We can also ask that about ourselves, do we help to improve other people or do we make them dull? Our goal should be to build relationships with people that will help to build us up and to be that kind of person for others.