[murphE]

Yes, the truth that God is Trinity, Father son and Holy Ghost, cannot be known by reason alone, but can be known by divine revelation.

God has revealed Himself as such, and to accept the testimony of the One who can neither deceive nor be deceived is quite reasonable.

[murphE]

oops! of course, son should be Son!

[malakhi]

God has revealed Himself as such

That again is entirely a matter of belief.