The psalmist as he spiritually seeks higher ground has in Psalm 120 honestly acknowledged his spiritual destitution, his inability to do anything about it, and the need for help. In Psalm 121:1-2 he refocuses to the hills, the location of God's house, a place he knows he can find help. In verses 3-8 it appears he is considering the difficulties involved in journeying to God's house! When the struggling saint needing help purposes to get back into church the devil will be sure to show you why you shouldn't or can't. In verses 3-8 it appears the psalmist deals with each difficulty to be faced.
In verse 3 it is as if the devil tells him the road is dangerous in places and you possibly could fall and injure yourself, but he reminds himself that "the LORD will not suffer thy foot to be moved."
In verse 4 he may be considering the danger while sleeping, but reminds himself that the LORD never sleeps
In verses 5-6 his God will protect him from the elements and weather he will face.
In verse 7 his God will protect him from all evil!
In verse 8 his God will protect him both in his journey to and back from Jerusalem.
The psalmist has considered the dangers of going to Jerusalem, and knowing his God is able to protect him in every situation maintains his resolve or determination to go. In other words, he has no reason for not going to the house of God. Dear saint, neither do you!