'Of the Flesh' in the Bible

but ye know that because of an infirmity of the flesh I preached the gospel unto you the first time:

But I say, walk by the Spirit, and ye shall not fulfil the lust of the flesh.

Now the works of the flesh are manifest, which are these : fornication, uncleanness, lasciviousness,

For he that soweth unto his own flesh shall of the flesh reap corruption; but he that soweth unto the Spirit shall of the Spirit reap eternal life.