Are the ordinances of the temple really necessary? Could we not just conform our lives to good principles and achieve the same ends?
Let’s start in the 84th Section of the Doctrine and Covenants, verse 19:
“And this greater priesthood administereth the gospel and holdeth the key of the mysteries of the kingdom, even the key of the knowledge of God.” [D&C 84:19]
The “key of the mysteries” is the right [keys] to administer the mysteries, meaning, the right to administer the ordinances. Hugh Nibley said:
“…but that is what Christ meant by the mysteries of the kingdom. He meant ordinances, which were necessary; and these he revealed to the apostles during his very confidential teachings of the forty days after the resurrection.” 
If you accept what Nibley is saying, Doctrine and Covenants 84:19 is equating the ordinances with the ability to know God. As is plainly stated in the next verse:
“Therefore, in the ordinances thereof, the power of godliness is manifest.”
What is this “power of godliness” that is given in the ordinances? Power to do what? Verse 22:
“For without this no man can see the face of God, even the Father, and live.”
If we ever wish to see God, the ordinances must be done, because that is where the power is manifest. That is where the pre-earth covenant is renewed, and salvation is dispensed.
[1 - Hugh Nibley, Temple and Cosmos: Beyond This Ignorant Present, Deseret Book, pg. 28.]