The first step in any building is the foundation. In the building of God, Peter tells us that Jesus Christ himself is the "chief cornerstone" of the foundation. This implies that everything in God's building depends on who Christ is, what He has done, and who He is in us. This truth has vast implications, and is a key factor in determining whether a gathering of people is in fact a "household of God."
If we consider the working of God in the Old Testament, I believe we see that everything pointed to the coming of Christ and the work He would do. When Christ completed the work of redemption, God rested from His labor. Our access into the presence of God is based solely on the work of God in Christ. We cannot add to or remove anything from what Christ has accomplished. In fact, if we try to add to what God has done, we move off the foundation of Christ. This is what happened to the Galatians. They tried to add something to what Christ had done, to make themselves more secure before God. Instead of making their standing more secure, they removed themselves from the foundation. Paul said they had "fallen from grace" and been "severed from Christ" (Galatians 5:1-6).
While we may wonder how the Galatians could be so blind, we need to realize that adding circumcision is not the only way we can move off the foundation of Christ. Other things may be more subtle and more likely to deceive us. We may try to add an ordinance (such as baptism or the Lord's table) as a requirement. These have their place in God's plan, but practicing these things does not secure our relationship with God. Some may add a certain standard of dress or diet. Others may add diligent effort in soul winning or some kind of service (such as ministry to the poor). God may (and will) lead us in these things, but doing them to make ourselves more acceptable to God can never be our motivation. We stand secure before God on one thing only: faith in Christ and His finished work on Calvary.
When we speak of faith, we are not defining it as simple intellectual belief. Faith is authored in our hearts by the word of God and results in fruit to the glory of God. The foundation of God is Christ and what He has done, and faith brings the benefit of His work into every member of the household. Christ's work opened the door for us to receive and live in the very life of God. Our access by Christ into the presence of God and the continual supply of His Spirit are realized as we walk by faith (Galatians 3:1-9). True faith causes "rivers of living water" to flow out of our hearts.
We may think about the foundation of Christ in two ways. One is the message that is held before the assembly. The other is whether the message has taken hold in the members so that they are secure on the foundation. Both are necessary if the house is to have a foundation on which to be built. A faulty message will be void of the anointing and blessing of God, and without these, there can be no building. Members who have not believed God and the word He has spoken to them will not be stable and grounded in the grace of our Lord Jesus Christ. They will not be secure on the foundation of Christ. Truth (Christ) must prevail in every member as a foundation and basis for building, before there can be progress in God's building.