Moses, as leader of the Israelites, wanted nothing more than to lead his country to victory over the Amaleks. 
He needed to rely on the strength of God. 
For Moses the strength of God came in the form of Aaron and Hur offering to hold up his hands while Joshua and the Israelites fought for their country. 
The help came from the Lord and so did the victory. 
Relying on the strength of God doesn’t mean that you reject the help of others or the resources God has given you. Instead it means that you look for and then accept what God provides for you. 
May we never become so prideful that we reject the provisions of God because it comes in the form of help from others.