'Taking Thought'

means,

Being anxious, very careful, concerned, and over-eager to obtain something.
"Take no thought", would then
mean, "Don't worry, be anxious,
or overly careful, concerned
or eager to obtain'.
Which of you by taking thought
can add one cubit unto his stature?
And why take ye thought for raiment?
Consider the lilies of the field, how they grow;
they toil not, neither do they spin:
And yet I say unto you,
That even Solomon in all his glory
was not arrayed like
one of these.

Matthew 6:  
27-29  
  
Therefore I say unto you,
Take no thought for your life,
what ye shall eat, or what ye shall drink;
nor yet for your body, what ye shall put on.
Is not the life more than meat,
and the body than raiment?
Behold the fowls of the air: for they sow not,
neither do they reap, nor gather into barns;
yet your heavenly Father feedeth them.
Are ye not much better    
than they?   

Matthew 6:   
25-26