In Scripture (James 2:23), Abraham is referred to as the friend of God.
Abraham was far from perfect. When a ruler of the land found his wife Sarah to be attractive, he told him she was his sister because he feared that ruler. She was his half-sister, but he concealed that she was his wife.
God promised him an heir. Because both he and his wife were old, she was beyond child bearing age, she suggested that he sleep with her servant. He did. Ishmael was born as a result.
God had instructed him to leave his land and all his relatives, but he took his nephew along.
Abraham messed up often. But, at the most important times, when God put him to the test, he followed through. He frequently misunderstood God, but he always believed. He was loyal.
Once he understood that he was to have an heir by Sarah, he followed through. Isaac was born in their old age.
When he faced the most important test, when God asked him to sacrifice Isaac, he believed in God enough to follow through. We see in Hebrews 11:19 that he believed that if he did put his son to death that God would raise him from the dead.
When he failed, it was because of fear or because he misunderstood the instructions. When it mattered most, he trusted God. He followed through. That is why God considered him a friend.
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