“Then again Abraham took a wife, and her name was Keturah. And she bare him Zimran, and Jokshan, and Medan, and Midian, and Ishbak, and Shuah. And Jokshan begat Sheba, and Dedan. And the sons of Dedan were Asshurim, and Letushim, and Leummim. And the sons of Midian; Ephah, and Epher, and Hanoch, and Abida, and Eldaah. All these were the children of Keturah.
And Abraham gave all that he had unto Isaac. But unto the sons of the concubines, which Abraham had, Abraham gave gifts, and sent them away from Isaac his son, while he yet lived, eastward, unto the east country.
And these are the days of the years of Abraham’s life which he lived, an hundred threescore and fifteen years. Then Abraham gave up the ghost, and died in a good old age, an old man, and full of years; and was gathered to his people. And his sons Isaac and Ishmael buried him in the cave of Machpelah, in the field of Ephron the son of Zohar the Hittite, which is before Mamre; the field which Abraham purchased of the sons of Heth: there was Abraham buried, and Sarah his wife.
And it came to pass after the death of Abraham, that God blessed his son Isaac; and Isaac dwelt by the well Lahairoi.” Genesis 25:1-11 (KJB)
Abraham was a man greatly blessed by God. It was not because he was a perfect man, neither without sin; rather it was because of His faith in God, and the faith that worked.
Did you notice the age of Abraham when he died? 175 years of age (“an hundred threescore and fifteen years”). He had six more sons through Keturah his new wife; and then more through concubines.
The blessings were God’s given by mercy and grace.
“For by grace are ye saved through faith; and that not of yourselves: it is the gift of God: not of works, lest any man should boast.
For we are His workmanship, created in Christ Jesus unto good works, which God hath before ordained that we should walk in them.” Ephesians 2:8-10