1. First Council of Nicaea (325)

Condemned Arianism and adopted the original Nicene Creed, fixed Easter date; recognized primacy of the sees of Rome, Alexandria and Antioch and granted the See of Jerusalem a position of honor.

2.First Council of Constantinople (381)

Condemned Arianism and Macedonianism, revised the Nicene Creed in regard to the Holy Spirit.

3.Council of Ephesus (431)

Condemned Nestorianism, proclaimed the Virgin Mary as the Theotokos ("God-bearer"), condemned Pelagianism, and reaffirmed the Nicene Creed.

4.Council of Chalcedon (451)

Condemned monophysitism, adopted the Chalcedonian Definition, which described the hypostatic union of the two natures of Christ, human and divine. Reinstated those deposed in 449 and deposed Dioscorus of Alexandria.

5.Second Council of Constantinople (553)

Condemned the Three Chapters as Nestorian, and condemned certain writings of Origen of Alexandria.

6.Third Council of Constantinople (680-681)

Condemned Monothelitism.

7.Second Council of Nicaea (787)

Restored the veneration of icons and condemned iconoclasm.

Obviously, there is a lot of terminology (theological jargon) in these explanations. Do you want to know more? Do you want to study the significance of these councils? Click here