Are you a Doctor of Divinity? Do you believe that you possess some special knowledge of the nature of God that only you are qualified or compelled to dispense to others? (Serious question and I'm not being snide when I ask it.)
Why would an omnipotent God need me to convince you that I am right about Him? (Serious question...)
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Great questions......

I will simply respond to this by saying God, through the Bible says that it is our duty as Christians to tell others about Him.
Mark 16:15 to the apostles, And He said to them, “Go into all the world and preach the gospel to every creature.
1 Peter 3:15, But sanctify the Lord God in your hearts, and always be ready to give a defense to everyone who asks you a reason for the hope that is in you, with meekness and fear;
2 Timothy 4:2, Preach the word! Be ready in season and out of season. Convince, rebuke, exhort, with all longsuffering and teaching.
Romans 10: 13-14, 3 For “whoever calls on the name of the Lord shall be saved.”
How then shall they call on Him in whom they have not believed? And how shall they believe in Him of whom they have not heard? And how shall they hear without a preacher?
As to why God NEEDS us to spread his word, I don't believe he NEEDS us to do anything, I believe that's what He CHOSE. Jesus chose common men like fishermen to spread his gospel, not Doctors of Divinity (The Pharisees). I'm just a common man myself.