Be Strong
Being Strong in the LORD means we are trusting in the LORD, and we are not trusting in anything else. David killed Goliath when he was trusting in the LORD, not himself. We can be strong in the LORD when we trust God, not ourselves. Compare the first 9 words of Luke 1:80 with the first 9 words of Luke 2:40 - These words are exactly the same. Luke 1:80 speaks about John the Baptist and Luke 2:40 speaks about Jesus Christ. Both had to grow physically, and as both grew physically, both waxed (grew) stronger in the spirit. This is exactly how we should be.
