on spiritual life and growth

"Now the parable is this: The seed is the word of God." (Luke 8:11 ESV)

"Take care then how you hear, for to the one who has, more will be given, and from the one who has not, even what he thinks that he has will be taken away.” (Luke 8:18 ESV)

On growth in the Christian's spiritual life, Herman Bavinck writes... 

The spiritual life implanted in regeneration is similar to the natural life in that it must be nourished and strengthened for it to expand and grow. In other ways there is a great difference between them, of course, inasmuch as the spiritual life originates in God as Savior, is acquired by the resurrection of Christ, and is eternal life that can neither sin nor die. Nevertheless, regenerate persons continually need to be "strengthened in their inner being with power through God's Spirit" (cf. Eph. 3:16). This strengthening of the spiritual life, like its beginning, originates with God and the riches of his grace. The life of spiritual persons, also after its origination, cannot for a moment be separated from God and his fellowship; in the same strict and particular sense in which this life is from God, it also is through and for him. It is he who nourishes and maintains it, never abandons it, prompts it to engage in certain activities, and not only bestows the capacity but also the willing and the working according to his good pleasure (Phil. 2:13; 2 Cor. 3:5). It is a life in communion with Christ. 

The spiritual life, though mysteriously and untraceably implanted in humans by the Spirit (John 3:8), is nevertheless from the beginning -- the moment it becomes conscious of itself -- bound to the Word of God. After all, it originated, even in the case of children, in the circle of the covenant of grace and in the gospel dispensation. In the internal calling, this spiritual life was called into being by an all-powerful word of God, a word, however, that he spoke in and through Christ. And it is born of that Spirit, who in the new life immediately implants the power to believe, writes the new law in one's heart, and internalizes the word of God (cf. "the implanted word" of James 1:21; 1 Pet. 1:23). When the spiritual life grows, it grows up in rapport with that word, which in various forms of instruction and admonition comes to a child in the home and, by virtue of its own nature, feels bound to that word that now comes through to the ear and the heart in intelligible sounds. 

The inexpressible word that was written in the human heart learns to know itself by the word that Christ speaks in Scripture. There is here a natural congeniality inasmuch as the Spirit testifies that the Spirit is truth. Just as a plant is bound up with the soil in which it is rooted and from which it draws its nourishment, so also the spiritual life is by virtue of its very nature bound up with Scripture. The external and the internal calling belong together and share the same word. But just as the external calling is not by itself sufficient to bring about the birth of the spiritual life, so also in bringing about increase and growth it is not sufficient by itself. The internal calling, accordingly, does not happen just once and stop when it has called the new life into being, but it continues indefinitely. Just as at the beginning God first created all things by the word and then upholds all things by the same word, so also the internal calling is active in the maintenance and development of the spiritual life. Believers are those who are called (Rom. 1:6), those who share in the heavenly calling (Heb. 3:1), who are perpetually called by God to his kingdom until they have in fact inherited it (1 Thess. 2:12; 5:24).

Now in Scripture the act by which the Holy Spirit causes us to understand the word of Christ in its spiritual sense and content and opens our consciousness to the truth is called by the particular term "enlightenment." Since sin has darkened the mind (Rom. 1:21; 1 Cor. 1:21; 2:14; Eph. 4:18; 5:8), what is needed is a renewal of the mind (Rom. 12:2; Eph. 4:23). This renewal is accomplished by God, who by revelation takes away from a person the hindrance that up until that time blocked the true understanding of things (Matt. 11:25; 16:17; Gal. 1:16). He does this by bestowing the Holy Spirit, who is a spirit of wisdom and revelation (Eph. 1:17), leads in all truth (John 16:13), teaches all things (14:26; 1 John 2:20), and enables us to understand the things of God (1 Cor. 2:10-16). Just as at the creation God, by his word of power, caused light to shine out of darkness, so by his Son (Matt. 11:27) and by the Spirit he shone in the hearts of people (2 Cor. 4:6) and enlightened the eyes of the heart (Eph. 1:18). 

-- Herman Bavinck, Reformed Dogmatics, IV:98-99