Jesus spoke about those things that people were confused about in scripture. The people in 1st century Jerusalem understood perfectly and agreed with the Biblical teaching on sexual immorality so he didn't HAVE to speak to them about it.
Romans 1:27 And likewise also the men,leaving the natural use of woman, burned in their own lust one toward another, men with men working what is unseemly, and receiving in themselves that recompense of their error which was meet.
John 1:1 In the beginning was the Word, and the Word was with God, and the Word WAS God. (Jesus IS the Word)
ALL Scripture is Inspired / God Breathed. It is the Inspired Word of God. Jesus is God and all the Scripture, both new and old, are His Words and His commands.