Abraham believed the Lord, and he counted it to him as righteousness. - Genesis 15:6

Since the days of Abraham, faith has been - and continues to be - the foundation of Christianity, and of each Christian’s life.

The time is fulfilled, the kingdom of God is at hand; repent and believe in the Gospel. - Mark 1:15

Jesus began His ministry with these words, and continued His earthly life calling for faith: in Himself, in His Father, God, and in the Kingdom of God.

So: what is faith?

The assurance of things hoped for, the conviction of things not seen. - Hebrews 11:1

We can have faith in someone or something, recognising that these things are real, true, genuine and valuable.  We can also have faith that relies and trusts the things believed in.  In this, we can believe the concept that God exists and that He is good; we can also go deeper, and be-living on God and His Word, relying on His presence in our life, etc.  The Christian requires both kinds of faith.

Faith is always personal.  Someone cannot believe for, or instead of, someone else - God has children, but no grandchildren.  This does not preclude a church community - rather, any form of church community, any real unity, must start and end based on the faith of each individual believer.  Our ability to stand together in prayer and song to God is based on us being able to also say these things individually.

Lord, I believe… - Mark 9:24

It should go without saying that a faith that is not expressed is a faith that cannot save.  We are able to have faith in God’s existence, but this doesn’t mean that we are living our lives for God.  Rather, we need to act according to our faith.  Like any muscle needs use to grow, for our faith in God to grow, we must live a life of faith - in this way, the smallest, faintest measure of faith can grow to encompass each of us.  When we fully trust God, many things that we couldn’t imagine, can happen.