I'm way behind with these!
1 Unless the LORD builds the house, its builders labor in vain.
Unless the LORD watches over the city, the watchmen stand guard in vain.
2 In vain you rise early and stay up late,
toiling for food to eat— for he grants sleep to those he loves.
3 Sons are a heritage from the LORD, children a reward from him.
4 Like arrows in the hands of a warrior are sons born in one's youth.
5 Blessed is the man whose quiver is full of them.
They will not be put to shame when they contend with their enemies in the gate.
Why is this a favourite passage?
Although the second half of the psalm might seem to run against it, I see this as one of the most explicit and practical psalms describing what it means to trust in God. The first two clauses emphasise a common Psalmic theme of trusting only in God rather than our own strength (or the strength of a horse, or princes or anything else). This is the practical outworking of idolatry - whenever we put our final trust in something other than God it ends up not just failing but betraying that trust. The next clause is one that challenges me often when we read this psalm in the Daily Office, and it is a more personal attack on idolatry - the idolatry of autonomy (a very common one today). Those who believe in God need to allow him to be God, to actually be in charge of heaven and earth - and therefore believers need to worry less (as Jesus taught).
The Psalm then seems to change gear with its recommendation of having children young, with the very practical consequence of having able bodied men to support you if - as a middle aged man - you end up in an argument 'at the gate'. I can recognise the practicality of this, but how it links with the foregoing is not yet clear to me.
Great psalm though.