Many Christians and most Pentecostals and charismatics are Pharisees. They have taken scripture and (pun intended) made it gospel. They have written their own laws and if you don't adhere to them your salvation is suspect.
You pray silently? God doesn't hear you. You don't speak in tongues? You're not filled with the Holy Spirit.
These people are so dogmatic in their beliefs that they can't see the grace of God at work in someone's life. They require signs and procedures. In becoming non-denominational they have created their own denomination. Rather than freeing themselves through the truth in Christ, they have forged more chains to bind themselves.
The grace and mercy of God is not bound by rules. Don't try to make more rules that get in the way.
I pray silently a lot and I enjoy the most profound presence of God when I do. I rarely speak in tongues and I am spirit-filled.
The grace of God is unending and ever surprising. Don't try to limit it.