Theodore Beza: Taking hold on Christ by faith produces fruit within us

Theodore Beza explains the work of the Spirit in our hearts and fruits in our lives as we take hold upon Christ in faith (note: these subjective, internal works of God within us -- regeneration and sanctification -- are to be distinguished from the objective, external declaration of righteousness by God in justification, which is grounded in the imputed righteousness of Christ alone, not the imperfect process of sanctification and increased Christ-likeness throughout our lives):

Now, the effects which Jesus Christ produces in us, when we have taken hold of Him by faith, are two. In the first place, there is the testimony which the Holy Spirit gives to our spirit that we are children of God, and enables us to cry with assurance, "Abba, Father". (Rom 8:16; Gal 4:6). In the second place, we must understand that when we apply to ourselves Jesus Christ by faith, this is not by some silly and vain fancy and imagining, but really and in fact, though spiritually (Rom 6:14; 1 John 1:6; 2:5; 3:7). In the same way as the soul produces its effects when it is naturally united to the body, so, when, by faith, Jesus Christ dwells in us in a spiritual manner, His power produces there and reveals there His graces. These are described in Scripture by the words 'regeneration' and 'sanctification', and they make us new creatures with regard to the qualities that we can have (John 3:3; Eph 4:21-24). (Theodore Beza, Faith and Justification)