[MMM]

Human Life gains luster and strength only when it is Human Life gains luster and strength only when it is polished and tempered..

I don't understand how what this has to do with combining two sentences.

There are a couple ways you could go approach this sentence.

polished and tempered　じゃないと　Human Life　は　luster and strength　を　gain　することができません。

Human Life　は　polished and tempered　だったっら　luster and strength　を　Gain　します。

Nagoyankee may have some better answers for you, but they will be in Japanese.

Just curious, why do you need to translate this sentence?