We do enter into a covenant at baptism, or why would be talk about 'baptismal vows' - which are, in modern times, renewed at the Easter Vigil every year by those who attend. They don't have the same canonical force as the vows of marriage or of religious life. However, in accepting baptism we do pledge ourselves to live a Christian life. That is one reason for the historical practice of a long catechumenate. In the (traditional) Roman rite, this is ennunciated in the rejection of Satan, his works and his empty promises, and by the turning to Christ - testified to by Tertullian and also by St. Basil among the Greeks.
"Let therefore the candidate for baptism declare thus in his renunciation: 'I renounce Satan and his works and his pomps and his worship and his angels and his inventions and all things that are under him'. And after his renunciation let him in his consociation say: 'And I associate myself to Christ and believe and am baptized into one unbegotten being'", etc.
St. Justin Martyr says that baptism was only given to those who promised to live a Christian life - the Greeks use the formula "I surrender myself to thee, O Christ, to be ruled by thy precepts" which about covers it.
However, what I would say to the candidate for reception into full communion is that while baptism entails a covenant, it is also more than that - the indwelling of the Holy Spirit is not to be sniffed at. Baptism brings us into the Church, but being part of the Church also means becoming a son or daughter of God the Father. This is only possible because we are, from the very moment we are baptised, caught up into the divine life. Which is totally awesome. The other thing is that, just as in the old covenant with Israel (or that with Abraham, to whom the promise was given rather than the Law), God remains faithful even if we don't. His promise is not rendered null and void if we slip up - that's why we have the sacrament of reconciliation. I think I'd also stress that, assuming the person was baptised correctly, they already have this divine life - the beginnings of 'heaven'.