The Lord’s servant, as he goes forth on his journey, committing himself to Jehovah alone 

If David wrote this psalm, then on lifting up his eyes as a gesture of prayer to the hill of Zion where the Ark rested, he was looking to Christ for his help. But by faith he would also be looking through that to the everlasting hills and the mountain of holiness, where God everlastingly dwells. One with such creative genius and power, who made the heavens, can well keep our lives and prevent our feet from sliding. There is no sun or moon with Him, for day and night are alike, and He needs no rest. So it is that He is eternally vigilant over His people. 

As mortals, we are subject to all the blights of life. Yet the sun or moon, representing afflictions or powers, shall not so smite us as to overthrow our faith or peace. The Lord, from His heavenly abode, watches over the comings and goings of each of His children.