We only obey Christ by believing? Even demons believe, they will not be saved. Paul's belief, prayer, fasting, etc did not save him. It wasn't until as Ananias said, "What are you waiting for, arise, be baptized and wash your sins away, calling on the name of the Lord." There is only one thing that saves- and that is Christ's blood- which we come in contact with through baptism. Romans 6:3- "Or don't you know that all of us who baptized into Christ Jesus were baptized into His death." In His death is where He shed His blood.
Belief baptizes us into Christ? The only way we get IN Christ is we are baptized INTO Christ as Romans 6:3 says. Yes water baptism. 1 Peter 3:21 says this baptism saves us. If baptism does not save us, then God is made out to be a liar, cause He says it does.
Partaking of of the Lords Supper is religious nonsense? It is our covenant in His blood. He says, "I tell you the truth, unless you eat of the flesh of the Son of Man and drink His blood, you have no life in you."
Remain faithful. No, if you miss taking the Lords Supper one Sunday you will not die, but if you did indefinitely you would. It's like when you cut of circulation to your foot and it falls asleep, and when it returns it hurts, but the tissue is not dead, because the absence of blood flow was temporary. But if you tied a rubber-band tightly around your finger and cut off blood flow so long that it turns gangrene and falls off, the tissue has died and can never be part of the body again. In the same way, spiritually speaking, life is in Christ's blood and we must stay in contact with it, faithfully until you die.
Repenting is an ongoing thing. We must put forth effort to turn away from our sins, otherwise we'd be living in sin like the world does, and to love the ways of the world is to hate God.
Why is it so hard for you to grasp the concept that our obedience does not earn grace, but God only gives grace to those who actively try to obey Him? God will not save one just because he believes. They would not call Jesus Lord Lord if they didn't believe, nor would they do things in His name. But he will say to them, depart from Me you who practice lawlessness (they did not OBEY His laws!) Don't you see that you must obey? Nothing we could possibly obey could earn us salvation, but it is only given to those who obey His commands. No, one has ever done so perfectly- and that's where grace comes in, but we only get that gift if we are trying. Effort is the evidence of love. "If you love Me you WILL obey what I command."