The Reason

According to Paul, paraphrased by Eugene Peterson:

We can only keep going, after all, by the power of God, who first saved us and then called us to this holy work. We had nothing to do with it. It was all His idea, a gift prepared for us in Jesus long before we knew anything about it. ... So keep at your work, this faith and love rooted in Christ... Guard this precious thing placed in your custody by the Holy Spirit who works in us.