13:9 know in part. The gifts of knowledge and prophecy at that time had conveyed only a part of God’s intended revelation to His people. In fact, the only earlier epistles by Paul were Galatians, I and II Thessalonians. Eventually, however, more would be forthcoming through the various apostles and prophets.
13:10 that which is perfect. “That which is perfect” cannot refer to Christ at His second coming, for “that” is a neuter pronoun. Since the previous verse refers to the incompleteness of the divine revelation at that time, “that which is perfect [that is, “complete”] almost certainly refers to the completion of Biblical revelation, as finally announced by John, the last of the apostles (Revelation 22:18-19). We now have all the prophetic truth needed in the Scriptures for the guidance of the church until Christ comes again. With few, if any, exceptions, we also have all the attestation we need to its veracity and power, so there is little need any more for miraculous signs, even though many still desire them.