National Australia Bank chief Andrew Thorburn has decided to buy back public trust in his scandal-fraught company by sparing more than 900,000 home borrowers a rate hike this month.The bank will hold its variable rate mortgage for owner-occupiers at 5.24 per cent - a significant discount to its three major rivals that have all announced repricings in the past fortnight.Thorburn last night pitched the rate-hold decision as a free gift to NAB's mortgage customers and a demonstration of NAB's desire to mend its breaches of public trust."We need to rebuild trust over time by listening and acting differently," he said."Our bank is based on our customers - their loyalty is really important to us and we need to appreciate them more."The NAB boss acknowledged that additional wholesale funding pressures had been carried by the bank since early this year, but hinted that they might not have been as great as other banks claimed."We are not immune to market and funding conditions and there has been some pressure there," he said. Estimates published by bank analysts at Goldman Sachs suggest that the 20 basis point rise in the spread of the 90 Bank Bill Swap Rate against the Overnight Indexed Swap rate reduced NAB's net interest margin by around two bps this year.The impact was heavier on Westpac, which stood to lose about four bps on its NIM before it signalled its intention to reprice its mortgage lines by 14 bps later this month.The repricings by Westpac, CBA and ANZ will more than recoup the higher funding costs, with most analysts last week boosting their 2019 earnings per share forecasts for each of these banks by at least 2 per cent.Put another way, the upgrades equate to more than a A$600 million top-up of the combined cash profits of the three banks. While NAB shareholders will miss out on such earnings gains, they might make it up anyway if the pricing discount induces a flood of new homebuyers to enter loan contracts with the bank.There was little evidence yesterday in the performance of NAB's share price against its peers that the decision to hold mortgage rates had seriously undermined its comparative profit outlook.NAB closed down 18 cents or 0.6 per cent, more or less in line with ANZ (down 0.5 per cent) and Westpac (down 0.4 per cent).Thorburn did not say how long borrowers would be shielded from the recent funding pressures weighing on the bank."The longer we can hold the rate the greater the benefit they get," he said.However, there are two factors now at play that indicate NAB might desist from passing on any rate rise this year.The first is that the rate spread between the 90-day bank bill and the OIS has narrowed significantly since peaking at 61 bps in June.Contraction of the spread has accelerated in the last week to around 40 bps.So, the funding pressure is already easing.A second factor, concerning NAB's strategic repositioning in the mortgage market, suggests the discount pricing might be here to