Which he shed on us abundantly through Jesus Christ our Saviour; Which - the Holy Spirit.
He shed, х execheen (G1632)] - 'poured out:' not merely gave (Acts 2:17-18; Acts 2:33): not only on the church in general, but also "on us" individually. This pouring out of the Spirit comprehends the grace received before, in, and subsequently to, baptism.
Abundantly, х plousios (G4145)] - 'richly' (Colossians 3:16). Through Jesus Christ - the channel of the Holy Spirit. So the Divine Three combine in our salvation. Our Saviour - immediately, as the Father is immediately. The Father is the Author of salvation, and saves us by Jesus.