Luke:
Obadiah gives us at least one clue and reason as to why they were "hated" by God.
"Ther pride of your heart has decieved you, you who live in the clefts of the rocks and make you home on the heights. You say to yourself, Who can bring me down down to the ground? (3-4)
It is not for me to say what if any sin God detests more than another, but "pride" sure seems to be something God really despises. The kind of pride which causes one to say in his heart, "I acknowledge you not, god."
The Sins of Israel
Murder and Idolatry - Ezekiel 22:3-6
Israel's evil and God’s destruction makes them a laughing stock among the nations - Deuteronomy 28:37; Psalm 44:13; Jeremiah 18:16; 24:9; Daniel 9:16
Israel's kings have promoted murder - Nehemiah 9:34; Isaiah 1:23; Micah 3:1-3, 9-11
Make light of mother and father - Exodus 21:17; Deuteronomy 27:16; Proverbs 20:20; 30:17
Oppressed strangers, mistreated orphans and widows - Exodus 22:21-22; Deuteronomy 27:19; Jeremiah 7:6; Zechariah 7:10
Despised the worship of God and His Sabbath - Leviticus 19:30; Amos 8:4-6; Ezekiel 22:26; Malachi 1:6-8, 12
Slander to cause murder - Leviticus 19:16; Deuteronomy 27:24; I Kings 21:10-13; Psalm 50:20; Jeremiah 9:4; Matthew 26:59; Acts 6:11-13
Fornication while worshiping idols - Deuteronomy 27:15; Psalms 106:28; Exodus 32:6
Incest - Leviticus 18:7-9, 15; 20:11-12, 17; Deuteronomy 27:20, 22-23
Violating the laws of uncleanness - Leviticus 18:19; 20:18
Adultery - Leviticus 18:20; 20:10; Jeremiah 5:8
Bribery - Exodus 23:8; Deuteronomy 16:19; 27:25
Usury - Exodus 22:25; Leviticus 25:35-36; Deuteronomy 23:19; Psalm 15:5
Extortion - Proverbs 1:19; Isaiah 56:11; I Corinthians 5:11; 6:10
Forgetting God - Deuteronomy 32:18; Psalm 106:21; Jeremiah 3:21
Yet..
Deuteronomy 7:6 says, "For you are a people holy to the LORD your God. The LORD your God has chosen you out of all the peoples on the face of the earth to be his people, his treasured possession."
Why?
8 For it is by grace you have been saved, through faith—and this is not from yourselves, it is the gift of God— 9 not by works, so that no one can boast.