So why am I so bold about saying that prayer is essential activity? I say that because, while Jesus Christ accomplished all of the work needed for our salvation, we accept that work based, largely, on prayer. It is not a requirement for salvation, but it is our activity in salvation.
Here's what I mean:
Romans 10:13 says, "For everyone who calls on the name of the Lord will be saved." Again, I'm not saying that it is required for salvation, but anyone who carries out the activity of prayer, in order to express their belief (an acknowledgment of which is required-Rom 10:9), will not be turned away. Paul is quoting Joel 2:32 in this verse.
In fact, prayer is often the way we lead someone to a saving knowledge of Christ, isn't it? We ask them to pray the "sinner's prayer." Yes, there is some controversy over that in recent years, and I agree with much of it. Yet, at it's heart, the sinner's prayer is simply an acknowledgement that I am a sinner in need of grace and that God has supplied the necessary sacrifice on my behalf.
It is an essential activity in receiving salvation, but it is not essential for salvation.
So while we acknowledge that it is Jesus who did everything we needed for salvation, it is our prayer that acknowledges this and our prayers that connect us with God in our relationship. Prayer is an essential activity, and I'm afraid many people don't take it seriously enough!