This is a False Teaching of the church of man. Just as Christ died on the Cross ONCE for all. Christ Blood covers All PAST Sins, Once for All.
And here are the Words from the Holy Spirit Christ Jesus as proof.  
Romans 3:24-26 (KJV)
24  Being justified freely by his grace through the redemption that is in Christ Jesus: 25  Whom God hath set forth to be a propitiation through faith in his blood, to declare his righteousness  
for the remission of sins that are past,
through the forbearance of God;  
26  To declare, I say, at this time his righteousness: that he might be just, and the justifier of him which believeth in Jesus.  
Hebrews 10:26-27 (KJV)
26  For if we sin willfully after that we have received the knowledge of the truth, there remained no more sacrifice for sins, 27  But a certain fearful looking for of judgment and fiery indignation, which shall devour the adversaries.  
1 John 3:9-10 (KJV)
9  Whosoever is born of God does not commit sin; for his seed remained in him: and he cannot sin, because he is born of God.  
10  In this the children of God are manifest, and the children of the devil: whosoever doeth not righteousness is not of God, neither he that loveth not his brother.  
11  For this is the message that ye heard from the beginning, that we should love one another.  
There are many people who call themselves Saved Christians, who believe as you have stated, and are in for a rude awaking when Christ comes.
For as it is written;  
Matthew 7:21-23 (KJV)
21  Not everyone that saith unto me, Lord, Lord, shall enter into the kingdom of heaven;
but he that doeth the will of my Father which is in heaven.  
22  Many will say to me in that day, Lord, Lord, have we not prophesied in thy name? and in thy name have cast out devils? and in thy name done many wonderful works?  
23  And then will I profess unto them, I never knew you: depart from me, ye that work iniquity.