Old Testament faith

What do we do with these genocidal passages, and how do we reconcile this presentation of YHWH with the God Jesus called Father? Marcion, the heresiarch-of-choice of the homoians, later declared heretical themselves, was probably influenced by passages such as these. Trinitarians should perhaps pause to reconsider these "awkward" passages in a new light. Without these stories, Marcion's contribution to the chain of events building to Nicea might have been absent. 

Joshua 6

21 They devoted the city to the LORD and destroyed with the sword every living thing in it—men and women, young and old, cattle, sheep and donkeys.

Deuteronomy 20:16-21
16 However, in the cities of the nations the Lord your God is giving you as an inheritance, do not leave alive anything that breathes. 17 Completely destroy[a] them – the Hittites, Amorites, Canaanites, Perizzites, Hivites and Jebusites – as the Lord your God has commanded you. 18 Otherwise, they will teach you to follow all the detestable things they do in worshipping their gods, and you will sin against the Lord your God.

1 Samuel 15:2-20

2 This is what the Lord Almighty says: ‘I will punish the Amalekites for what they did to Israel when they waylaid them as they came up from Egypt. 3 Now go, attack the Amalekites and totally destroy[a] all that belongs to them. Do not spare them; put to death men and women, children and infants, cattle and sheep, camels and donkeys.’”

4 So Saul summoned the men and mustered them at Telaim—two hundred thousand foot soldiers and ten thousand from Judah. 5 Saul went to the city of Amalek and set an ambush in the ravine. 6 Then he said to the Kenites, “Go away, leave the Amalekites so that I do not destroy you along with them; for you showed kindness to all the Israelites when they came up out of Egypt.” So the Kenites moved away from the Amalekites.

7 Then Saul attacked the Amalekites all the way from Havilah to Shur, near the eastern border of Egypt. 8 He took Agag king of the Amalekites alive, and all his people he totally destroyed with the sword. 9 But Saul and the army spared Agag and the best of the sheep and cattle, the fat calves[b] and lambs—everything that was good. These they were unwilling to destroy completely, but everything that was despised and weak they totally destroyed.

10 Then the word of the Lord came to Samuel: 11 “I regret that I have made Saul king, because he has turned away from me and has not carried out my instructions.” Samuel was angry, and he cried out to the Lord all that night.

12 Early in the morning Samuel got up and went to meet Saul, but he was told, “Saul has gone to Carmel. There he has set up a monument in his own honor and has turned and gone on down to Gilgal.”

13 When Samuel reached him, Saul said, “The Lord bless you! I have carried out the Lord’s instructions.”

14 But Samuel said, “What then is this bleating of sheep in my ears? What is this lowing of cattle that I hear?”

15 Saul answered, “The soldiers brought them from the Amalekites; they spared the best of the sheep and cattle to sacrifice to the Lord your God, but we totally destroyed the rest.”

16 “Enough!” Samuel said to Saul. “Let me tell you what the Lord said to me last night.”

“Tell me,” Saul replied.

17 Samuel said, “Although you were once small in your own eyes, did you not become the head of the tribes of Israel? The Lord anointed you king over Israel. 18 And he sent you on a mission, saying, ‘Go and completely destroy those wicked people, the Amalekites; wage war against them until you have wiped them out.’ 19 Why did you not obey the Lord? Why did you pounce on the plunder and do evil in the eyes of the Lord?”