It is in vain that you rise up early
and go late to rest,
eating the bread of anxious toil;
for he gives to his beloved sleep.
Remember, in the first verse it starts off, "Unless the Lord build the house..." That idea has carried over into this verse. We are still talking about house building.
Anxious toil is that worrisome sort of work. It is that work that is based in your own worries. Doing extra things to try to calm that rumbling fear. Getting up early and going to bed late, hoping that you will cover all of your bases, that all of your ducks will be in a row...
To his beloved, God gives rest. There is peace in the houses that He builds.