In the Paschal Homily delivered by St. Gregory Palamas on Holy Saturday (Homily 16), he mentions on page 122 (Paragraph 16)
The grace of the Son, of His Father and of the Spirit came to dwell in the baptismal water, such that when it touched those baptized later following His example, they would be divinely regenerated, and mystically renewed and re-created in such a way that they would be born of the new Adam and so have God's blessing, not being of the will of the flesh, nor of the will of man, but of God through Jesus Christ (John 1:13).
Does this mean that all those baptized by St. John the Forerunner after the Baptism of Christ were truly sanctified by the waters of the Jordan? Were Christ's Disciples baptizing using the Trinitarian formula and triple immersion or was this done only after Christ's death and resurrection?
Look at the Bright Saturday Gospel reading: John 3: 22-33
22-24 After these things Jesus and His disciples came into the land of Judea, and there He remained with them and baptized. Now John also was baptizing in Aenon near Salim, because there was much water there. And they came and were baptized. For John had not yet been thrown into prison.
25-26 Then there arose a dispute between some of John's disciples and the Jews about purification. And they came to John and said to him, "Rabbi, He who was with you beyond the Jordan, to whom you have testified--behold, He is baptizing, and all are coming to Him!
John 4:1-2
Therefore, when the Lord knew that the Pharisees had heard that Jesus made and baptized more disciples than John (though Jesus Himself did not baptize, but His disciples, ...
Would Christ have given Holy Communion and Holy Orders (do this in remembrance of Me) to His Apostles at the Last Supper had they not been baptized beforehand? After His Resurrection, Christ gave His Apostles the power to forgive sins. But it was not until Pentecost that they received the fullness of the Holy Spirit.
Reference: Saint Gregory Palamas: The Homilies, Ed. and Trans. by Christopher Veniamin, Mount Thabor Publishing, 2009.