is an offering of a sacrifice or thankgiving; it also refers to the thing or things offered. Shakespeare's sonnets are about a young man (a poet) and his love life. Sonnet 125 shows that for the poet, love is not a matter of external pride — that is, he is not interested in his rivals' self-frustrating displays of false love.
In the third quatrain, the poet's offering to the youth is neither "mixed with seconds" nor "knows no art"; his affection is pure love, not like the artificial posturing of his rivals:
No; let me be obsequious in thy heart,
And take thou my oblation, poor but free,
Which is not mix'd with seconds, knows no art,
But mutual render, only me for thee.