Spiritual growth outside of the Church is impossible.
A great article can be found here…and an excerpt as follows:
…The gospel is good news. The message determines the medium. There is a clear logic to Paul’s argument in Romans 10, where he contrasts “the righteousness that is by works” and “the righteousness that is through faith.” We were redeemed by Christ’s actions, not ours; the Spirit applies this redemption to us here and now so that we are justified through faith apart from works; even this faith is given to us through the proclamation of Christ. Since this gospel is a report to be believed rather than a task for us to fulfill, it needs heralds, ambassadors, and witnesses.
The method of delivery is suited to its content. If the central message of Christianity were how to have your best life now or become a better you, then we wouldn’t need heralds, but rather life coaches, spiritual directors, and motivational speakers. Good advice requires a person with a plan; good news requires a person with a message. This is not to say that we do not also need good advice or plans, but that the source of the church’s existence and mission in this world is this announcement of God’s victory in Jesus Christ.
Coaches can send themselves with their own suggestions, but an ambassador has to be sent with an authorized announcement. If the goal is to get people to go and find Christ, then the methods will be whatever we find pragmatically successful; if it’s all about Christ finding sinners, then the methods are already determined. Simply quoting verses 13-15 reveals the logical chain of Paul’s argument: “‘For everyone who calls on the name of the Lord will be saved.’ But how are they to call on him in whom they have not believed? And how are they to believe in him of whom they have never heard? And how are they to hear without someone preaching? And how are they to preach unless they are sent?” The evangel defines evangelism; the content determines the methods of delivery; the marks of the church (preaching and sacrament) define its mission (evangelizing, baptizing, teaching, and communing).
The marks of the true church are the proper preaching of the Word, administration of the sacraments, and discipline. The mission of the church is simply to execute these tasks faithfully. Throughout the Book of Acts, the growth of the church is attributed to the proclamation of the gospel: “The word of God spread.” Waking the dead, this gospel proclamation is not only the content but the method. Those who believed were baptized along with their whole household. They were not simply added to the conversion statistics, but to the church-the visible church, which is no more visible in this world than when it is gathered around the Lord’s Table in fellowship with their ascended head. Furthermore, the apostles and elders-and, by Acts 6, the deacons-served the church as officers representing Christ’s threefold office of Prophet, King, and Priest…
…In this way, Christ makes himself not only the gift, but the giver; not only the object of faith, but the active agent, together with the Spirit, in giving us faith. And he not only gives us this faith in the beginning, but deepens, matures, and increases our faith throughout our lives. The gospel is not something that we need to “get saved” so that we can move on to something else; it is “the power of God unto salvation” throughout our pilgrimage. So we need this gospel to be delivered to us regularly, both for our justification and our sanctification…