A Muslim may ask:
Trinity is blasphemy. God is one not three. Check your math 1+1+1=3 not 1. How come you say God is one and the same time three?
Since you are visiting our web site, I assume you are using a computer, and I assume you at least know a little about it. Using these assumptions, I will try to explain to you the Trinity in a computer illustration.
A computer usually consists of: case (hardware), operating system (software), monitor, keyboard, and mouse. Most importantly, the computer needs electricity to work, without it, the computer is dead.
We believe God exist by himself (Father), spoken by His Word (Son), and alive by His Spirit (Holy Spirit). This is the Trinity you reject.
No illustration is perfect, but we are trying to make this concept of Trinity easier for you to understand.
Imagine God (the Father) is the computer case (the hardware), and what we call God Son is the operating system and all other applications (software), and the Holy Spirit is the electricity which make this computer functioning.
We definitely do not need a monitor, keyboard, or a mouse for the computer case to work as a stand alone (i.e. a server like the one this web site is hosted on, the server does not have to have a monitor and other peripherals for it to work).
We know that a hardware (mother board, processor, hard disk, etc…) can not do anything without having a software installed in it. Also we know that the hardware and the software will not interact and work without the electricity being plugged into the hardware.
Still we call all of these three parts of the computer, a computer, it is not three computers.