Ambrose of Milan

She ascends leaning on the Word of God. For those who are more perfect recline upon Christ, just as John also was reclining at Jesus' bosom. So then she either rested in Christ or reclined upon him or even—since I am speaking of a marriage—as if already given into the power of Christ, she was led to the bridal couch by the bridegroom.

On Isaac and the Soul 8.72 ↗

Jerome

O mortal, you have now been cleansed in baptism, and it is said of you, "Who is she that comes up, cleansed and leaning upon her beloved?" so that she, indeed, is cleansed, but she is not able to guard her purity, unless she is sustained by the Lord God. You, who but a moment ago were freed from your sins, how is it that you desire to be delivered by the mercy of God, if not in the way I stated, that, when we have done everything, we confess that we of ourselves are insufficient?

Against the Pelagians 3.15 ↗

Bede

Under the apple tree, I awakened you, etc. The apple tree most aptly symbolizes the wood of the holy cross, on which He deigned to hang for the salvation of all; about which the Church said above in praise, "As an apple tree among the trees of the woods, so is my beloved among the sons." Under the apple tree, therefore, the Lord awakened the Synagogue, which He recalled from eternal death through the faith in His Passion. …

Commentary on the Song of Songs ↗