There are only two environments in which you can live. The first is the sin environment, and the second is the spiritual environment. The vast majority of humanity lives in the sin environment, because most people do not understand the difference between the two, and are not interested in pursuing a daily study in order to learn the differences between the two environments.
The sin environment, which we typically refer to as being out of fellowship, is the environment in which your spiritual life does not function. The sin environment is a separation from a relationship with God. The sin environment offers false views of life, and is one of helplessness and hopelessness, which are oftentimes not recognized, because the individual lacks the necessary knowledge, in order to see the reality of their situation.
This Psalm has been describing the burdens and hopelessness of the sin related environment.
And now in verse 15, the recognition of that hopelessness, and the solution of that hopelessness, are described.
In the sin environment, there is no one and nothing that you can turn to, or speak to, or reach out to, in order to help you in life.
There is only one source of help in all of creation, and that is God, through Christ, by means of the Holy Spirit.
And thus the call to God, because God is the only one that can hear, and the only one who can solve the helpless situation.
To wait on the Lord, is the recognition that God is the only course of action that is available to the individual believer in Christ.
To wait on sin, in contrast, is a wait forever for nothing to happen.
Therefore, waiting on the Lord, is the correct direction of one’s attention, and focus on the only true solution in life.
God is the sovereign authority over all that exists, and the only higher authority that can hear your prayer, and answer it.
The confession of sin, is a form of prayer, which is offered to God the Father, the result of which is immediate restoration into fellowship.
Fellowship is the spiritual environment, in which the spiritual life functions. And that is where you should be living your life, moment by moment, day by day.