We all know what kind of animals leeches are: parasites. We know that they (literally) feed off the bodies of others. They take the nutrition and energy of their host without giving anything back. And, to suck the life out of someone, they use their mouths.
There are parasites in the spiritual world also. We've all met them~people that, when the conversation ends, we feel drained, both physically and spiritually. Just as physical leeches hang onto their victims by their mouth, so does the spiritual one.
A lot of the spiritual parasites are well-meaning, helpful, and generous people, Christians included. But there is a twist~a contradiction~between their actions and their words. The Bible says that we Christians should edify one another; that is, to lift one another up. (Romans 14:19) Paul says in 1 Cor. 10:23 that we are free to do or say anything, but not all things done in free will edify another person.
James spells it out for us in the third chapter of his book. A horse is turned by a bit and a ship by a wheel (vv.3-4) , but both are small compared to the body being driven. The key factor is: the part that a person controls tells the horse or ship where to go. In verse 5, he points out that the tongue is a small part of our body, yet boasts great things. Out of our mouths come both blessings and cursings. (v.10a)
The parasitic person has bitterness, envying and strife in their hearts, and comes from earthly, natural and devilish sources. (vv.14-15) Romans 14:17 tells us the parasite may speak well, but the other person is not edified. How can one person edify another if their conversation is all about lifting themselves up? James tell us these things ought not to be. (3:10b)
The next time we are in a conversation with another person, let's pay attention to our end of it. Are we guilty of leech speech? Proverbs 27:1-2 says not to boast of tomorrow, because we do not know what it will bring. Let someone else praise us, not our own mouth. Let a stranger tell of our good deeds, not our own lips.
We must be careful; the pride in us brings contention. (Proverbs 13:10) Isaiah 14:13-14 tells us about the king of Babylon, how he wanted to be 'like the most high.' If we are lifting up anyone but Christ, then we are doomed to fall. It was that kind of rebellion that got Lucifer cast out of heaven. (Ezek. 31:10-11)
As soon as we take our eyes off of God and focus on self, then we are falling into the same trap as Adam and Eve. We should not keep on eating of the fruit that they ate of, but instead opt for the spiritual fruit. These are, according to Gal. 5:22-23, love, joy, peace, longsuffering, gentleness, goodness, faith, meekness and temperance.
I don't see a reference to self in there anywhere.