God as a shield is a rather common reference in many Psalms, such as 5:12, 7:10, 18:30, 28:6-7, 59:11, 91:4 and 144:2.
In addition see Genesis 15:1.
The spirit of this song can come only from those who thankfully receive each day as a gift from God’s hand. Our World Belongs to God, paragraph 44 teaches, “Life is a gift from God’s hand” which we receive thankfully “with reverence for the Creator...” (paragraph 44).
The call for God’s help in our daily living arises from those who are confident of his fatherly care; consider reading Belgic Confession, Article 13 and Heidelberg Catechism, Lord’s Day 9, Question and Answer 26.