Psalm 127 thematically breaks into two parts. In verses 1-2, security and significance are addressed by noting the vanity of self-reliance (see the commentary). The idea of security is expressed with images of watching over, watchmen, and sleep. The concept of significance is stated negatively in terms of vanity. But significance is possible when the Lord builds the house, and watches over the city.
In the second part of the psalm, verses 3-5, the psalmist addresses security and significance in terms of children. The idea of significance is seen in the language of children as one’s heritage, reward, and blessing. Children are a blessed reminder that we matter if for no other reason that our children need us. In ministry, one often deals with very broken and damaged people. In talking with such people, those that are parents often confess that they believe that their children are the one thing right about their lives. And although it can be taken to unhealthy extremes when a parent tries to live too vicariously through their children, children do allow us to find significance in passing on a legacy to the next generation. The idea of children as a means of security seems a bit odd in our culture. After all, parents are to provide security for the child. But in the past and to some degree now, children were a means to provide security for aged parents in a world where social safety nets were practically non-existent. In this sense children would be a means of security.
Thankfully this psalm not only surfaces the desire for security and significance but it ultimately points us in the direction of God’s providence as its source. It is God, and God alone, who provides true security and lasting significance. He does through providentially overseeing our lives and through blessings like children.