Or HaChaim on Genesis 11:32/אור החיים על בראשית י״א:ל״ב

1 ויהיו ימי תרח חמש שנים ומאתים שנה. Terach lived to be 205 years. The reason the decription of Terach's age differs from the description of the other people listed in this chapter, i.e. "all the days of so and so were, etc." is twofold. It can either mean that Terach lived longer than the years originally allocated to him, or it can mean that he did not live all the years that had originally been allocated to him. Here the absence of the words "all the days of his life" most likely mean that he lived longer than the years originally allocated to him. He accumulated merit because of his extraordinary concern for the welfare of his son Abraham. One proof may be seen when we compare Terach's lifespan with that of his father Nachor. The latter had only lived for a total of 148 years (11,24-25). Terach lived 57 years longer than his father. Our sages (Bereshit Rabbah 65,12) have said that when a man approaches to within 5 years (either side) of the age at which his parents died he should begin to be concerned about his own death approaching.

2Inasmuch as Terach lived many years longer than his father, the Torah reports his death in conjunction with his migration to Charan to indicate which merit added the extra years to his life. Had the Torah merely stated the usual "ויהיו כל ימי תרח, all the years of Terach were, etc., we would have assumed that G'd had originally allocated to him a lifespan of 205 years although this would have been quite wrong. There is also support from the text for the view that Terach lived fewer years than had been allocated to him originally. The Torah reports that he set out on his way to Canaan. However, the Torah also reports that he died in Charan which is on the way. Terach had failed to make good on his vow to move to Canaan and settled in Charan. G'd shortened Terach's lifespan because he did not make good on his vow.

3I have had an inspiration which enables me to explain why Abraham left his father in Charan though the latter had migrated for his sake all the way from Ur Casdim. When Abraham moved to Canaan Terach was 143 years old. He was 68 years old when Abraham was born and Abraham was 75 when he moved to the land of Canaan. [I presume that verse 26 which describes Terach as 70 years old when his three sons were born must refer to his age when the youngest was born. Ed.] It seems difficult to understand that Abraham abandoned his father for so many (62) years, even though G'd had told him לך לך.

4I believe the answer is simply that Abraham had good reason to expect that his father would die soon after his departure for Canaan, seeing that he was within 5 years of the age at which his grandfather Nachor had died. G'd may even have given Abraham a subtle hint when He told him לך לך, go on "your acccount." The words "on your account," were to indicate that even if Abraham's father were to live additional years he had only Abraham's merit to thank for those years. Abraham therefore did not have to blame himself for "abandoning" his aged father.