This is a 16th-century lullaby carol, and it's a Scottish translation of a poem by Luther, so we're some way here from the medieval English examples I've recently been posting; but this has become a Christmas standard, in settings by various composers, under the name 'Balulalow'.
Personally, I like it because I particularly love 'my dear heart' as a term of endearment - it's what Aslan calls Lucy in Voyage of the Dawn Treader! ;) It has such a gentle sound, here as in 'Myn Lyking'.
These two verses are an extract from the longer 'Ane Sang of the birth of Christ' from the wonderfully-named Ane Compendious Buik of Godly and Spirituall Sangis, compiled in 1567 by the brothers James, John and Robert Wedderburn. (You can find the whole poem here). So if you've ever wondered what medieval Scots looked like, here's an example:
O my deir hert, young Jesus sweit,
Prepare thy creddill in my spreit,
And I sall rocke thee in my hert,
And neuer mair from thee depart.
But I sall praise thee euermoir,
With sangs sweit unto thy gloir;
The knees of my hert sall I bow,
And sing that richt Balulalow.
O my dear heart, young Jesus sweet,
Prepare thy cradle in my spirit
And I shall rock thee in my heart
And never more be parted from thee.
But I shall praise thee evermore
With songs sweet unto thy glory;
The knees of my heart shall I bow
And sing that true Balulalow. ('Lullaby')
Here's Benjamin Britten's setting from his 'Ceremony of Carols':