Without a doubt, it was Daniel's faith in God. (1John 4:18) says "Perfect Love cast out all fear"(when someone comes to the realization than God loves them so much that He gave his only begotten Son to save them, they cease to fear anything) that would include lions. Because if God did not spare his only begotten Son but gave him up for us, how will God with his Son, not give us all other things?). It is a shame and nearly impossible to truly believe that God gave us the (greatest He had) His only begotten Son Jesus Christ) and then would hold back something smaller from us. As it is written, "If God be for us, what can be against us" (that can prevail long-term)? The answer is nothing. Daniel neither feared the Lions or king Darius,because of his faith in God strengthened by his (matured understanding) of God's love for him, in whom he believed. It is the will of God that his children (not just Daniel) live free of (all) fear, including the fear of death. If we still fear, it is because (the love of God has not yet been perfected in us) we have not yet come to the (full) understanding of how much God loves us. When we have (complete)l understanding) of Gods (perfect love) for us, that (revelation) will keep us from fearing anything in this world. And you are right the hills are coverd with God's Angels. And Psalms 91:11 says, "God gives his angels charge over us to keep us in (all) our ways" unlike the prophets servant, we don't have to see them (to know they are there) it is enough for us, that God's Holy Word tells us they are there. It is the same reason we do not fear this movie we are watching. Because God has already told us How It ends. 🙏