The excellence of a fruit is always a sign of the quality of the tree which bore it. In the case of St. Joachim, the Immaculate Conception of Mary reflects a splendid glory on the chaste union of her parents.
The Gospels speak of a sister of Our Lady who accompanied her even to the foot of the Cross. According to some authorities she too was a daughter of Anna and of Joachim.
His feast was first introduced into the Breviary by Julius II, who fixed the date of March 20. Leo XII (Joachim Pecci) raised it to a double of the second class. In the reform of the Breviary carried out by Pius X, August 16th was the date fixed.
The close relationship which existed between the Savior and St. Joachim confers on the latter of great dignity, raising him above other saints, to that the honor paid to him is reflected upon Christ Himself in a special manner and upon His Immaculate Mother. They loved him and honored him in this world above all others. Their love is like a precious gem which adorns the crown of the holy Patriarch in heaven.
(Source: The New Roman Missal, Rev. F. X. Lasance)