The Letter or the Spirit?

Which is more important?  The letter or the Spirit of the law?  Here is a Scripture that addresses the issue

2 Corinthians 3:6(NKJV)

6who also made us sufficient as ministers of the new covenant, not of the letter but of the £Spirit; for the letter kills, but the Spirit gives life.

The reason I bring this up is that the accepted dogma is that we have to specifically ask Jesus to come into our lives to receive salvation.  The whole believe in your heart and speak it with your mouth thing.

But I have found other Scriptures where Jesus is speaking and He seems to say something different.  Here is an example.

Luke 10:25-28(NKJV)

25And behold, a certain lawyer stood up and tested Him, saying, “Teacher, what shall I do to inherit eternal life?”

26He said to him, “What is written in the law? What is your reading of it?”

27So he answered and said, “‘You shall love the Lord your God with all your heart, with all your soul, with all your strength, and with all your mind,’ £ and ‘your neighbor as yourself.’”£

28And He said to him, “You have answered rightly; do this and you will live.”

Here it seems to be saying, love God and be a good person.  Jesus says "...do this and you will live.".  So which is it?

2 Corinthians 3:16-18(NKJV)

16Nevertheless when one turns to the Lord, the veil is taken away. 

17Now the Lord is the Spirit; and where the Spirit of the Lord is, there is liberty. 

18But we all, with unveiled face, beholding as in a mirror the glory of the Lord, are being transformed into the same image from glory to glory, just as by the Spirit of the Lord.

I'm not sure this adds any clarity to it but here is my take on the whole thing. 

Jesus seems to focus a lot on the heart.  Where is your heart.  If your heart is right I believe that Jesus will call it good.  But why take the chance.  Say the words, accept Jesus and remove any doubt.  You'll be glad you did!