Context and Background:
Exodus 17:15 is situated within the narrative of the Israelites' journey through the wilderness after their exodus from Egypt. This chapter recounts two significant events: the provision of water from the rock at Rephidim and the battle against the Amalekites. The latter event culminates in Moses building an altar and naming it "The LORD Is My Banner."

The Battle Against the Amalekites:
The Amalekites, a nomadic tribe, attacked the Israelites at Rephidim. Moses instructed Joshua to choose men and engage in battle while he stood on the hill with the staff of God in his hand. As long as Moses held up his hands, the Israelites prevailed; when he lowered them, the Amalekites gained the upper hand. Aaron and Hur supported Moses' hands, ensuring the Israelites' victory.

The Altar and Its Significance:
Following the victory, Exodus 17:15 states, "And Moses built an altar and named it The LORD Is My Banner." The Hebrew name for the altar is "Yahweh Nissi." This act of building an altar was a common practice in the Old Testament, serving as a memorial to God's intervention and faithfulness.

Theological Implications:
1. Divine Sovereignty and Protection: The naming of the altar underscores the belief in God's sovereignty and His role as protector and leader of His people. The term "banner" signifies a rallying point or standard, symbolizing God's presence and guidance in battle.

2. Faith and Dependence on God: The narrative highlights the importance of faith and reliance on God for victory. Moses' act of raising his hands is symbolic of prayer and dependence on divine power rather than human strength.

3. Community and Support: The support of Aaron and Hur illustrates the necessity of community and mutual support among believers. It emphasizes the idea that spiritual battles are not fought in isolation but require collective effort and encouragement.

4. Remembrance and Worship: The altar serves as a tangible reminder of God's deliverance and a place of worship. It calls the Israelites to remember God's past faithfulness and to trust Him for future challenges.

Historical and Cultural Context:
In the ancient Near Eastern context, altars were often erected to commemorate significant events or divine encounters. The naming of the altar as "The LORD Is My Banner" reflects a common practice of attributing victories to divine intervention, a theme prevalent throughout the Old Testament.

Application for Believers:
For contemporary believers, Exodus 17:15 serves as a reminder of God's unchanging nature as a protector and provider. It encourages Christians to look to God as their banner in times of spiritual warfare and to rely on His strength rather than their own. The passage also calls for the establishment of spiritual "altars" in one's life—moments and practices that commemorate God's faithfulness and foster a spirit of worship and gratitude.