1.) They Don't Love Their Pastor. In the letter they always say they love their pastor, but their actions (writing an anonymous letter) tell a different story. Oh the irony. If you love your pastor talk to them like an adult...face to face.
2.) They Don't Know Their Bible. Did you know people who stretch out their hand against God's annointed servants will not go unpunnished. Individuals can justify their actions to men, but God, the JUDGE, knows their heart, thoughts, and secret motives. This is why pastors must pray for people who hurt them. This is why we pray, "Father forgive them, for they know not what they do." Also, sending anonymous letters shows zero respect and esteem for the leaders God has placed in your church. If you really love them "Speak the truth in love." Remembering though Ephesians 4:15 is not talking about "your truth" - that's your opinion. It is talking about speaking GOD'S TRUTH in whatever situation you are in.
1 Samuel 26:9-10
But David said to Abishai, "Do not destroy him, for who can stretch out his hand against the Lord's anointed and be without guilt?" NASU
1 Thessalonians 5:12-13
But we request of you, brethren, that you appreciate those who diligently labor among you, and have charge over you in the Lord and give you instruction, 13 and that you esteem them very highly in love because of their work. NASU
3.) They Are Self Centered. Every anonymous letter I have ever received only stated someone's opinion. It reflected their taste concerning Music, Facilites, Preaching Style, etc...
Philippians 2:3-5
Do nothing from selfishness or empty conceit, but with humility of mind regard one another as more important than yourselves; 4 do not merely look out for your own personal interests, but also for the interests of others. 5 Have this attitude in yourselves which was also in Christ Jesus. NASU
NEVER have I reveived an anonymous letter concerning Ecclesiology, Theology, or Doctrine. In other words: anonymous letters never have substance, only steam.
Suggestions for handling an anonymous letter.
You can usually tell what you are in for before you open the envelope.
After opening the letter first check for a signature. If there is no John Hancock at the bottom. CHUNK IT. Resist every temptaion to read it. Run...and I mean RUN to the shredder and feed it to the little paper eating monster in the corner. The shredder can handle it...you can't.