Trust in God, and only God

During the time of Isaiah, the Babylonian Empire was amassing forces on Israel's northern border. An invasion seemed imminent. So what did the Israelites do? To whom did they turn for protection? Not God. Rather, they sought an alliance with their long-time nemesis, Egypt.

That's the background to Isaiah 30: 1:2 (ESV), in which God expresses his anger at the Israelites for putting their trust in earthly protection, rather than in God.

“Ah, stubborn children,” declares the Lord,
“who carry out a plan, but not mine,
and who make an alliance, but not of my Spirit,
    that they may add sin to sin;
who set out to go down to Egypt,
    without asking for my direction,
to take refuge in the protection of Pharaoh
    and to seek shelter in the shadow of Egypt!

The lesson is difficult, but important: Trust only in God. Do not trust in earthly schemes.

Now, that does not mean that, when sick, we must avoid doctors. Certainly, consult doctors when ill! Rather, the lesson is that we shouldn't trust doctors above God, because God works through doctors. Most importantly, God does everything according to his will. As Paul writes in 1 Corinthians 3:7 (ESV),

So neither he who plants nor he who waters is anything, but only God who gives the growth.