In "God's Word for Today" David Woods writes:
Four different terms to describe God are used in verses 1 and 2. … Psalms: A Bible Commentary in the Wesleyan Tradition states: “God is described using four different names: most High, Almighty, Lord, and my God. The first and second portray His power, the third His covenant relationship with Israel, the last His intimacy. Four terms are used to describe the place of safety: shelter, shadow, refuge, and fortress. The first suggests a place of secrecy; the second, shade; the third, shelter; and the fourth, a fortress or stronghold of God's power.” (p. 281)
Source: Studies in the Psalms: Adult Teacher's Insights, page 59.