Galatians 6:7-9:

Be not deceived; God is not mocked: for whatsoever a man soweth, that shall he also reap.
For he that soweth to his flesh shall of the flesh reap corruption; but he that soweth to the Spirit shall of the Spirit reap life everlasting.
And let us not be weary in well doing: for in due season we shall reap, if we faint not.

Notes on Galatians 6:7-9:

This is a spiritual law that will either work for you or against you.  If you choose to live in the flesh, you will reap corruption, which will certainly interfere with your healing.  On the positive side, if you sow to the Spirit by fellowshipping with God, reading and thinking about His Word and living right, you will reap the benefits of the life of God, including healing.  This is not talking about mere salvation, because Paul says that in due season we shall reap.  He is talking about receiving the benefits of the Spirit in this life.

This passage does not mean that you can sow good works and thereby “merit” healing.  Healing is based on 100% grace and 0% personal merit.  However, if you pray and read the Word, you will build yourself up so that you are able to walk in the privileges that eternal life gives you.  If you never pray but just indulge your flesh all evening watching TV, you will be dominated by your flesh, which will lead to corruption.

See also:

Am I Sick Because I Left a Door Open to the Devil?
Sickness as Chastening and Judgment in the New Testament
Paper Roadblocks to Healing
Healing and Repentance
Objection: God Wouldn’t Heal Paul’s Thorn in the Flesh
Objection: Teaching Grace Gives People a License to Sin