As iron sharpens iron, so one man sharpens another. --Proverbs 27:17 (NIV)
One of my favorite types of chemistry lab experiments in college involved a procedure called titration. The purpose of carrying out a titration is to be able to determine the strength of a solution. This is done by adding a bright purple colored chemical indicator to a beaker containing a colorless liquid of unknown concentration. Slowly and steadily, one drop at a time, the indicator is added to the colorless solution. Because of the way the chemicals react, the purple indicator doesn't have any visible effect on the solution until quite a bit of it has been added. The procedure is complete when the very faintest of color change is observed.
Outside of the chemistry lab I observed something similar in a social setting. I learned that whether we intend it to happen or not, we are all prone to be influenced in some way. People of strong godly character are able to make wise decisions about the company they keep. They surround themselves with friends who edify them, support their worldview, and encourage them to walk closely with God. Conversely, people without a strong connection to God or a personal relationship with him, often find themselves with fewer true, lasting friends. Without a firm foundation in Christ, these people live primarily for the world and its pursuits.
In both cases, people are being influenced. Like in the titration procedure, the resulting "color" of a person's character depends on the "indicator". As God's word says in 1st Corinthians 15:33, bad company corrupts good character. Sometimes this is immediately apparent, other times it happens slowly and gradually as bad choices give way to sinful behavior and eventual destruction.
The benefits of making good friends and the effect it has on character can sometimes be a gradual process too. It has been my personal experience that taking the time to get to know people well enough to form quality, meaningful friendships can be just as involved as carefully tending to a titration procedure. Fortunately, we don't have to worry about friendship being an exact science. As long as we are an active part of a body of believers and regularly gather together with others, we can be sure that we will be plenty of opportunities to meet people of godly character.