Acts 2:28 Thou hast made known to me the ways of life; thou shalt make me full of joy with thy countenance.
Peter, in His Pentecost Day sermon, quotes a Psalm of David prophesying the bodily resurrection of the Christ. Because of His resurrection, he is able to give us this promise: the Lord will make you full of joy in His presence.
The living and resurrected Lord Jesus Christ is by us, near us, with us, even in us. he lives to be with us always. His ”countenance” is the expression of His face. In the Benediction, “His countenance being lifted up” means His face is smiling on us. The face of God is the presence of God. Jesus is present with always for blessing, for our good. We don’t think about it most of the time, but when we remember His smiling presence with us it makes us full of joy. The very thought and reminder of the loving presence of God brings a smile to our face. And He will make us full of joy any time, especially in difficult times when we need Him most. Rejoice in the Lord, for He makes you joyful.