From time to time as a pastor, I encounter people who claim to be Christian and have no church home. They often ask for my opinion. Often they are content to go through life without any connection to a local church and without any accountability to a local body.
They assert something to the effect that they are under Jesus, being shepherded by him. They neglect the fact that the way Jesus shepherds his church is by appointing local shepherds in the a local body (1 Peter 5:1ff). Any Christian not connected to a local body and in submission to local church leaders is in a spiritually precarious position.
Sometimes a Christian will argue they are accountable to God directly therefore they will not be accountable to any human authority within the church. For some this supposedly makes their spiritual relationship more pristine. While it is true the church is not the mediator between God and man only Christ is. But the church is the body of Christ and in that body God gifts different gifts and points people in authority in order to build the body up and protect the body (Eph. 4:7-16)
Christians are not accountable to other people and human institutions instead of God or before God. Christians are accountable to other people and human institutions by the Word and will of God and in obedience to God.
So while the argument is valid that the ultimate authority in the Christian's life is God, the argument becomes fallacious when the argument is used to defend the unbiblical position that the Christian need not submit to earthly authority, either inside or outside the church—authorities which are instituted by God.
Any Christian who insists they answer to God and to God alone are not living by the parameters they've set for themselves. For if they truly see themselves as submitting to God's authority in their life and if they see themselves as answerable to God and as one who is actively obeying Him, then they would willingly submit to the earthly authority God has placed in their life—whether inside or outside the church.
The Christian’s accountability before God includes biblical accountability to secular governing authorities, brothers and sisters in Christ, and the leadership of a local church. Yes, there is only one Lawgiver and Judge; there is only One who can save and destroy, and that is God (James 2:10). That being said, the judgment of Almighty God will include how Christians respond and submit to the earthly authority God has placed in their lives.
It is often true in life that one of the visible marks of how well one submits to God is how well one submits to those that God has placed in authority in this world.
I once counseled someone that if they couldn't attend our church because of some doctrinal difference and concerns then they still needed to find some church somewhere and put themselves under the authority of the leaders God had raised up in that church. It is a mark of our submission to God that we submit to men God installs. Of course, we are to obey God rather than men when the two are in conflict, but this is a very rare occurrence. And the first step are not to proclaim our non-submission, but to Biblical confront in a manner that is loving. Sadly, some people use confrontation as a means to allow their own desire to not submit to leaders to burst out and explode under false justification.
God has ordained the church to be the body of Christ for all Christians. This means that Christians need to connect to some local expression of the body. It is for their good.