Adam Clarke on 1 Peter 1:8

Whom having not seen, ye love - Those to whom the apostle wrote had never seen Christ in the flesh; and yet, such is the realizing nature of faith, they loved him as strongly as any of his disciples could, to whom he was personally known. For faith in the Lord Jesus brings him into the heart; and by his indwelling all his virtues are proved, and an excellence discovered beyond even that which his disciples beheld, when conversant with him upon earth. In short, there is an equality between believers in the present time, and those who lived in the time of the incarnation; for Christ, to a believing soul, is the same to-day that he was yesterday and will be for ever.

Ye rejoice with joy unspeakable - Ye have unutterable happiness through believing; and ye have the fullest, clearest, strongest evidence of eternal glory. Though they did not see him on earth, and men could not see him in glory, yet by that faith which is the evidence of things not seen, and the subsistence of things hoped for, they had the very highest persuasion of their acceptance with God, their relation to him as their Father, and their sonship with Christ Jesus.