Notice that this section begins with the words “You are my portion, Lord. . . .” This is likely a reference to the way God gave portions of the promised land to the tribes of Israel (see Joshua 13-21). Allotments were given to all of the tribes except for the tribe of Levi, because God had dedicated the Levites to serve and lead in the worship of the Lord. Their service to God included everything from offering sacrifices to teaching the law, and from leading in worship to taking care of all the materials used for worship (see Exodus 25-30). As Joshua explained to the people, “The Levites . . . do not get a portion among you, because the priestly service of the Lord is their inheritance” (Joshua 18:7).
In a similar way, the psalmist has nothing and no one but God to depend on. The Lord is his portion, his inheritance. In utter dependence and trust, the psalmist takes everything to God in prayer, including his laments. With God as our portion, we too have the privilege of taking all our troubles and cares to the One whose guidance and instruction give us full life.