Hannah's faithfulness to her vow to give her only son to God is a powerful reminder that because God gave His only Son, everything we have and are belongs to God. Therefore we are also called to give back everything to God for His glory.
The setting of the book of Samuel, when there was no king in Israel, reminds us of how our cry for a king can be answered through Jesus, who desires to occupy the throne of our hearts.
To walk carefully in this world is to walk with wisdom, and to walk in wisdom means making the most of every opportunity we have, to redeem the time for the glory of God.
In contrast to popular ideas on spiritual warfare, the Bible teaches us that our main response to the Devil is not offensive, but defensive; we are called to resist him as we live, in word and deed, in light of Jesus' victory on the cross.