What I take from it is homosexuality is a mental disorder like we have other mental disorders. God can take away any mental disorder. To act on the mental disorder of homosexuality is a sin. Rational, sane thinking humans do not engage in sex acts with someone of the same sex. It’s not the way nature (God) wired us.
It is disordered behavior, against the natural order. One might or might not define that as "mental illness". Normally mental illness is not defined strictly in behavioral terms. Homosexuality includes a strong voluntary component, essentially 100%, very much unlike conventional mental illness. I personally believe homosexuality as as much or more "societal illness" as "mental illness", but with grave personal consequences both in the temporal life and beyond.