They were saying that they expected a stream of income from the hand of God. They were exchanging tangible treasure for intangible treasure, both in history and eternity. This is what Jesus had told His listeners to do. A person trusts the person to whom he swears allegiance. Even if he does not trust him, he nevertheless becomes dependant on him.
Covenantal allegiance is formal.
It is renewed by the Lord's Supper. When every member who owned real estate sold his property and gave the money to the church, they set an example. This example was based on trust in God to provide an alternative stream of income. It also involved trust in the apostles to use the money in a God-honoring way. The text says that as many people who owned real estate sold it and laid the money at the feet of the apostles.