Why does the Torah dwell so briefly on the ten generations from Noach until Avraham, and then, when it comes to Avraham, it dwells on his actions and descendants at length?
Rashi (to Bereishis 37:1): This can be compared to a pearl that dropped in the sand. The owner sifts the sand all around where it fell, filling the sieve with stones and pebbles, until he finds the pearl. Then he throws out the pebbles and retains the pearl. The pebbles symbolize the nations, and the pearl, Avraham Avinu.
Why is Terach's name repeated?
Bereishis Rabah: This is an indication that Terach did Teshuvah, and merited both Olam ha'Zeh and Olam ha'Ba. Refer to Shemos 3:4:151:1.